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 $157.32   10.818%   $174.3389   $174.34   $174.35   $174.30  
  Purchase #2 $46.89   7.284%   $50.3055   $50.31   $50.30   $50.30  
  Purchase #3 $244.89   9.715%   $268.6811   $268.68   $268.70   $268.70  
  Purchase #4 $95.67   13.227%   $108.3243   $108.32   $108.30   $108.30  
  Purchase #5 $84.83   9.773%   $93.1204   $93.12   $93.10   $93.10  
  Purchase #6 $9.62   13.691%   $10.9371   $10.94   $10.95   $10.90  
  Purchase #7 $244.82   5.741%   $258.8751   $258.88   $258.90   $258.90  
  7 purchase totals = $884.04       $964.5824   $964.59   $964.60   $964.50