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 $87.73   11.292%   $97.6365   $97.64   $97.65   $97.60  
  Purchase #2 $141.85   12.219%   $159.1827   $159.18   $159.20   $159.20  
  Purchase #3 $213.54   11.844%   $238.8317   $238.83   $238.85   $238.80  
  Purchase #4 $81.58   5.546%   $86.1044   $86.10   $86.10   $86.10  
  Purchase #5 $68.69   9.162%   $74.9834   $74.98   $75.00   $75.00  
  Purchase #6 $97.28   10.453%   $107.4487   $107.45   $107.45   $107.40  
  Purchase #7 $134.49   3.706%   $139.4742   $139.47   $139.45   $139.50  
  7 purchase totals = $825.16       $903.6616   $903.65   $903.70   $903.60