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 $94.53   9.775%   $103.7703   $103.77   $103.75   $103.80  
  Purchase #2 $118.73   6.634%   $126.6065   $126.61   $126.60   $126.60  
  Purchase #3 $35.29   12.378%   $39.6582   $39.66   $39.65   $39.70  
  Purchase #4 $115.47   11.305%   $128.5239   $128.52   $128.50   $128.50  
  Purchase #5 $246.63   10.828%   $273.3351   $273.34   $273.35   $273.30  
  Purchase #6 $11.45   10.115%   $12.6082   $12.61   $12.60   $12.60  
  Purchase #7 $66.63   11.709%   $74.4317   $74.43   $74.45   $74.40  
  7 purchase totals = $688.73       $758.9339   $758.94   $758.90   $758.90