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 $112.82   9.384%   $123.407   $123.41   $123.40   $123.40  
  Purchase #2 $57.92   13.871%   $65.9541   $65.95   $65.95   $66.00  
  Purchase #3 $84.38   12.564%   $94.9815   $94.98   $95.00   $95.00  
  Purchase #4 $165.64   12.150%   $185.7653   $185.77   $185.75   $185.80  
  Purchase #5 $202.67   8.438%   $219.7713   $219.77   $219.75   $219.80  
  Purchase #6 $119.71   4.407%   $124.9856   $124.99   $125.00   $125.00  
  Purchase #7 $176.83   8.192%   $191.3159   $191.32   $191.30   $191.30  
  7 purchase totals = $919.97       $1,006.1807   $1,006.19   $1,006.15   $1,006.30