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 $84.56   11.124%   $93.9665   $93.97   $93.95   $94.00  
  Purchase #2 $223.86   9.390%   $244.8805   $244.88   $244.90   $244.90  
  Purchase #3 $19.54   11.138%   $21.7164   $21.72   $21.70   $21.70  
  Purchase #4 $9.40   11.152%   $10.4483   $10.45   $10.45   $10.40  
  Purchase #5 $84.59   8.302%   $91.6127   $91.61   $91.60   $91.60  
  Purchase #6 $117.75   8.745%   $128.0472   $128.05   $128.05   $128.00  
  Purchase #7 $13.29   11.417%   $14.8073   $14.81   $14.80   $14.80  
  7 purchase totals = $552.99       $605.4789   $605.49   $605.45   $605.40