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 $51.41   6.368%   $54.6838   $54.68   $54.70   $54.70  
  Purchase #2 $194.37   13.313%   $220.2465   $220.25   $220.25   $220.20  
  Purchase #3 $21.96   7.172%   $23.535   $23.54   $23.55   $23.50  
  Purchase #4 $85.90   11.687%   $95.9391   $95.94   $95.95   $95.90  
  Purchase #5 $246.42   6.472%   $262.3683   $262.37   $262.35   $262.40  
  Purchase #6 $112.33   5.637%   $118.662   $118.66   $118.65   $118.70  
  Purchase #7 $68.99   13.853%   $78.5472   $78.55   $78.55   $78.50  
  7 purchase totals = $781.38       $853.9819   $853.99   $854.00   $853.90