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 $239.68   12.240%   $269.0168   $269.02   $269.00   $269.00  
  Purchase #2 $77.96   3.342%   $80.5654   $80.57   $80.55   $80.60  
  Purchase #3 $181.44   4.801%   $190.1509   $190.15   $190.15   $190.20  
  Purchase #4 $249.68   8.637%   $271.2449   $271.24   $271.25   $271.20  
  Purchase #5 $57.29   6.341%   $60.9228   $60.92   $60.90   $60.90  
  Purchase #6 $40.65   11.408%   $45.2874   $45.29   $45.30   $45.30  
  Purchase #7 $146.64   8.593%   $159.2408   $159.24   $159.25   $159.20  
  7 purchase totals = $993.34       $1,076.4290   $1,076.43   $1,076.40   $1,076.40