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 $66.26   13.361%   $75.113   $75.11   $75.10   $75.10  
  Purchase #2 $114.80   3.857%   $119.2278   $119.23   $119.25   $119.20  
  Purchase #3 $94.86   7.498%   $101.9726   $101.97   $101.95   $102.00  
  Purchase #4 $79.75   11.404%   $88.8447   $88.84   $88.85   $88.80  
  Purchase #5 $42.60   12.115%   $47.761   $47.76   $47.75   $47.80  
  Purchase #6 $189.86   4.837%   $199.0435   $199.04   $199.05   $199.00  
  Purchase #7 $174.25   9.814%   $191.3509   $191.35   $191.35   $191.40  
  7 purchase totals = $762.38       $823.3135   $823.30   $823.30   $823.30