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 $99.26   3.371%   $102.6061   $102.61   $102.60   $102.60  
  Purchase #2 $159.31   10.328%   $175.7635   $175.76   $175.75   $175.80  
  Purchase #3 $72.86   4.259%   $75.9631   $75.96   $75.95   $76.00  
  Purchase #4 $62.85   4.536%   $65.7009   $65.70   $65.70   $65.70  
  Purchase #5 $107.34   5.112%   $112.8272   $112.83   $112.85   $112.80  
  Purchase #6 $193.82   4.362%   $202.2744   $202.27   $202.25   $202.30  
  Purchase #7 $193.42   6.223%   $205.4565   $205.46   $205.45   $205.50  
  7 purchase totals = $888.86       $940.5917   $940.59   $940.55   $940.70