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 $37.48   10.239%   $41.3176   $41.32   $41.30   $41.30  
  Purchase #2 $210.87   11.127%   $234.3335   $234.33   $234.35   $234.30  
  Purchase #3 $224.31   11.503%   $250.1124   $250.11   $250.10   $250.10  
  Purchase #4 $115.31   5.276%   $121.3938   $121.39   $121.40   $121.40  
  Purchase #5 $159.46   13.631%   $181.196   $181.20   $181.20   $181.20  
  Purchase #6 $75.78   5.491%   $79.9411   $79.94   $79.95   $79.90  
  Purchase #7 $11.75   10.756%   $13.0138   $13.01   $13.00   $13.00  
  7 purchase totals = $834.96       $921.3082   $921.30   $921.30   $921.20