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 $223.46   10.361%   $246.6127   $246.61   $246.60   $246.60  
  Purchase #2 $94.25   3.565%   $97.61   $97.61   $97.60   $97.60  
  Purchase #3 $132.86   5.797%   $140.5619   $140.56   $140.55   $140.60  
  Purchase #4 $67.43   7.580%   $72.5412   $72.54   $72.55   $72.50  
  Purchase #5 $11.36   6.658%   $12.1163   $12.12   $12.10   $12.10  
  Purchase #6 $92.68   11.313%   $103.1649   $103.16   $103.15   $103.20  
  Purchase #7 $195.48   4.240%   $203.7684   $203.77   $203.75   $203.80  
  7 purchase totals = $817.52       $876.3754   $876.37   $876.30   $876.40