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 $58.26   3.138%   $60.0882   $60.09   $60.10   $60.10  
  Purchase #2 $43.79   11.108%   $48.6542   $48.65   $48.65   $48.70  
  Purchase #3 $80.48   8.378%   $87.2226   $87.22   $87.20   $87.20  
  Purchase #4 $108.96   11.265%   $121.2343   $121.23   $121.25   $121.20  
  Purchase #5 $185.71   11.111%   $206.3442   $206.34   $206.35   $206.30  
  Purchase #6 $229.61   12.204%   $257.6316   $257.63   $257.65   $257.60  
  Purchase #7 $20.80   9.722%   $22.8222   $22.82   $22.80   $22.80  
  7 purchase totals = $727.61       $803.9973   $803.98   $804.00   $803.90