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 $221.33   11.633%   $247.0773   $247.08   $247.10   $247.10  
  Purchase #2 $206.38   12.667%   $232.5222   $232.52   $232.50   $232.50  
  Purchase #3 $42.98   8.645%   $46.6956   $46.70   $46.70   $46.70  
  Purchase #4 $126.79   3.571%   $131.3177   $131.32   $131.30   $131.30  
  Purchase #5 $243.93   5.775%   $258.017   $258.02   $258.00   $258.00  
  Purchase #6 $246.49   6.176%   $261.7132   $261.71   $261.70   $261.70  
  Purchase #7 $29.50   9.364%   $32.2624   $32.26   $32.25   $32.30  
  7 purchase totals = $1,117.40       $1,209.6054   $1,209.61   $1,209.55   $1,209.60