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 $43.79   13.328%   $49.6263   $49.63   $49.65   $49.60  
  Purchase #2 $209.44   9.664%   $229.6803   $229.68   $229.70   $229.70  
  Purchase #3 $10.51   13.261%   $11.9037   $11.90   $11.90   $11.90  
  Purchase #4 $200.26   5.551%   $211.3764   $211.38   $211.40   $211.40  
  Purchase #5 $74.59   5.319%   $78.5574   $78.56   $78.55   $78.60  
  Purchase #6 $221.42   8.378%   $239.9706   $239.97   $239.95   $240.00  
  Purchase #7 $222.66   7.708%   $239.8226   $239.82   $239.80   $239.80  
  7 purchase totals = $982.67       $1,060.9373   $1,060.94   $1,060.95   $1,061.00