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 $84.79   13.381%   $96.1357   $96.14   $96.15   $96.10  
  Purchase #2 $200.88   9.833%   $220.6325   $220.63   $220.65   $220.60  
  Purchase #3 $156.46   10.391%   $172.7178   $172.72   $172.70   $172.70  
  Purchase #4 $123.37   12.733%   $139.0787   $139.08   $139.10   $139.10  
  Purchase #5 $32.69   7.126%   $35.0195   $35.02   $35.00   $35.00  
  Purchase #6 $31.36   3.836%   $32.563   $32.56   $32.55   $32.60  
  Purchase #7 $110.73   9.554%   $121.3091   $121.31   $121.30   $121.30  
  7 purchase totals = $740.28       $817.4563   $817.46   $817.45   $817.40