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 $43.49   13.854%   $49.5151   $49.52   $49.50   $49.50  
  Purchase #2 $238.35   11.407%   $265.5386   $265.54   $265.55   $265.50  
  Purchase #3 $174.65   4.547%   $182.5913   $182.59   $182.60   $182.60  
  Purchase #4 $70.69   7.172%   $75.7599   $75.76   $75.75   $75.80  
  Purchase #5 $249.58   8.595%   $271.0314   $271.03   $271.05   $271.00  
  Purchase #6 $87.60   11.370%   $97.5601   $97.56   $97.55   $97.60  
  Purchase #7 $218.48   7.203%   $234.2171   $234.22   $234.20   $234.20  
  7 purchase totals = $1,082.84       $1,176.2135   $1,176.22   $1,176.20   $1,176.20