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 $60.42   3.289%   $62.4072   $62.41   $62.40   $62.40  
  Purchase #2 $211.32   3.782%   $219.3121   $219.31   $219.30   $219.30  
  Purchase #3 $143.84   7.586%   $154.7517   $154.75   $154.75   $154.80  
  Purchase #4 $112.35   8.746%   $122.1761   $122.18   $122.20   $122.20  
  Purchase #5 $99.83   8.832%   $108.647   $108.65   $108.65   $108.60  
  Purchase #6 $213.57   4.286%   $222.7236   $222.72   $222.70   $222.70  
  Purchase #7 $66.79   10.823%   $74.0187   $74.02   $74.00   $74.00  
  7 purchase totals = $908.12       $964.0364   $964.04   $964.00   $964.00