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 $64.35   13.136%   $72.803   $72.80   $72.80   $72.80  
  Purchase #2 $118.37   4.392%   $123.5688   $123.57   $123.55   $123.60  
  Purchase #3 $98.66   3.339%   $101.9543   $101.95   $101.95   $102.00  
  Purchase #4 $220.94   6.343%   $234.9542   $234.95   $234.95   $235.00  
  Purchase #5 $189.84   9.366%   $207.6204   $207.62   $207.60   $207.60  
  Purchase #6 $160.39   8.823%   $174.5412   $174.54   $174.55   $174.50  
  Purchase #7 $22.57   4.528%   $23.592   $23.59   $23.60   $23.60  
  7 purchase totals = $875.12       $939.0339   $939.02   $939.00   $939.10