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 $176.66   11.799%   $197.5041   $197.50   $197.50   $197.50  
  Purchase #2 $114.63   10.550%   $126.7235   $126.72   $126.70   $126.70  
  Purchase #3 $187.76   3.589%   $194.4987   $194.50   $194.50   $194.50  
  Purchase #4 $232.79   11.688%   $259.9985   $260.00   $260.00   $260.00  
  Purchase #5 $53.41   10.427%   $58.9791   $58.98   $59.00   $59.00  
  Purchase #6 $5.93   6.381%   $6.3084   $6.31   $6.30   $6.30  
  Purchase #7 $81.30   3.447%   $84.1024   $84.10   $84.10   $84.10  
  7 purchase totals = $852.48       $928.1147   $928.11   $928.10   $928.10