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 $119.82   12.344%   $134.6106   $134.61   $134.60   $134.60  
  Purchase #2 $146.50   3.662%   $151.8648   $151.86   $151.85   $151.90  
  Purchase #3 $133.75   8.869%   $145.6123   $145.61   $145.60   $145.60  
  Purchase #4 $216.67   13.790%   $246.5488   $246.55   $246.55   $246.50  
  Purchase #5 $85.94   11.157%   $95.5283   $95.53   $95.55   $95.50  
  Purchase #6 $48.74   13.853%   $55.492   $55.49   $55.50   $55.50  
  Purchase #7 $43.62   10.315%   $48.1194   $48.12   $48.10   $48.10  
  7 purchase totals = $795.04       $877.7762   $877.77   $877.75   $877.70