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 $191.40   11.391%   $213.2024   $213.20   $213.20   $213.20  
  Purchase #2 $28.99   4.702%   $30.3531   $30.35   $30.35   $30.40  
  Purchase #3 $155.89   8.362%   $168.9255   $168.93   $168.95   $168.90  
  Purchase #4 $226.52   7.871%   $244.3494   $244.35   $244.35   $244.30  
  Purchase #5 $68.48   13.143%   $77.4803   $77.48   $77.50   $77.50  
  Purchase #6 $130.67   6.850%   $139.6209   $139.62   $139.60   $139.60  
  Purchase #7 $76.32   3.424%   $78.9332   $78.93   $78.95   $78.90  
  7 purchase totals = $878.27       $952.8648   $952.86   $952.90   $952.80