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 $228.68   12.786%   $257.919   $257.92   $257.90   $257.90  
  Purchase #2 $94.66   6.854%   $101.148   $101.15   $101.15   $101.10  
  Purchase #3 $68.43   10.202%   $75.4112   $75.41   $75.40   $75.40  
  Purchase #4 $183.50   11.596%   $204.7787   $204.78   $204.80   $204.80  
  Purchase #5 $71.62   9.862%   $78.6832   $78.68   $78.70   $78.70  
  Purchase #6 $244.55   11.866%   $273.5683   $273.57   $273.55   $273.60  
  Purchase #7 $137.44   9.110%   $149.9608   $149.96   $149.95   $150.00  
  7 purchase totals = $1,028.88       $1,141.4692   $1,141.47   $1,141.45   $1,141.50