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 $101.37   3.187%   $104.6007   $104.60   $104.60   $104.60  
  Purchase #2 $34.97   8.677%   $38.0043   $38.00   $38.00   $38.00  
  Purchase #3 $65.29   10.186%   $71.9404   $71.94   $71.95   $71.90  
  Purchase #4 $119.29   9.469%   $130.5856   $130.59   $130.60   $130.60  
  Purchase #5 $191.53   6.260%   $203.5198   $203.52   $203.50   $203.50  
  Purchase #6 $15.84   9.126%   $17.2856   $17.29   $17.30   $17.30  
  Purchase #7 $222.37   11.413%   $247.7491   $247.75   $247.75   $247.70  
  7 purchase totals = $750.66       $813.6855   $813.69   $813.70   $813.60