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 $61.61   11.339%   $68.596   $68.60   $68.60   $68.60  
  Purchase #2 $249.50   8.422%   $270.5129   $270.51   $270.50   $270.50  
  Purchase #3 $179.92   12.812%   $202.9714   $202.97   $202.95   $203.00  
  Purchase #4 $195.54   4.262%   $203.8739   $203.87   $203.85   $203.90  
  Purchase #5 $112.60   13.683%   $128.0071   $128.01   $128.00   $128.00  
  Purchase #6 $44.70   4.867%   $46.8755   $46.88   $46.90   $46.90  
  Purchase #7 $48.87   11.578%   $54.5282   $54.53   $54.55   $54.50  
  7 purchase totals = $892.74       $975.3650   $975.37   $975.35   $975.40