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 $46.80   6.778%   $49.9721   $49.97   $49.95   $50.00  
  Purchase #2 $199.41   8.492%   $216.3439   $216.34   $216.35   $216.30  
  Purchase #3 $16.26   8.139%   $17.5834   $17.58   $17.60   $17.60  
  Purchase #4 $97.87   13.516%   $111.0981   $111.10   $111.10   $111.10  
  Purchase #5 $233.72   10.356%   $257.924   $257.92   $257.90   $257.90  
  Purchase #6 $102.46   13.749%   $116.5472   $116.55   $116.55   $116.50  
  Purchase #7 $228.46   10.766%   $253.056   $253.06   $253.05   $253.10  
  7 purchase totals = $924.98       $1,022.5247   $1,022.52   $1,022.50   $1,022.50