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 $134.62   6.644%   $143.5642   $143.56   $143.55   $143.60  
  Purchase #2 $244.88   5.731%   $258.9141   $258.91   $258.90   $258.90  
  Purchase #3 $97.35   5.580%   $102.7821   $102.78   $102.80   $102.80  
  Purchase #4 $125.62   6.487%   $133.769   $133.77   $133.75   $133.80  
  Purchase #5 $225.57   9.845%   $247.7774   $247.78   $247.80   $247.80  
  Purchase #6 $200.90   7.183%   $215.3306   $215.33   $215.35   $215.30  
  Purchase #7 $94.27   9.580%   $103.3011   $103.30   $103.30   $103.30  
  7 purchase totals = $1,123.21       $1,205.4385   $1,205.43   $1,205.45   $1,205.50