Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $129.80   11.683%   $144.9645   $144.96   $144.95   $145.00  
  Purchase #2 $173.51   10.630%   $191.9541   $191.95   $191.95   $192.00  
  Purchase #3 $103.73   3.569%   $107.4321   $107.43   $107.45   $107.40  
  Purchase #4 $180.29   5.686%   $190.5413   $190.54   $190.55   $190.50  
  Purchase #5 $180.75   11.189%   $200.9741   $200.97   $200.95   $201.00  
  Purchase #6 $118.74   6.111%   $125.9962   $126.00   $126.00   $126.00  
  Purchase #7 $123.41   3.160%   $127.3098   $127.31   $127.30   $127.30  
  7 purchase totals = $1,010.23       $1,089.1721   $1,089.16   $1,089.15   $1,089.20