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 $232.82   6.746%   $248.526   $248.53   $248.55   $248.50  
  Purchase #2 $93.27   6.605%   $99.4305   $99.43   $99.45   $99.40  
  Purchase #3 $113.39   6.157%   $120.3714   $120.37   $120.35   $120.40  
  Purchase #4 $237.34   10.520%   $262.3082   $262.31   $262.30   $262.30  
  Purchase #5 $140.46   13.558%   $159.5036   $159.50   $159.50   $159.50  
  Purchase #6 $200.30   13.738%   $227.8172   $227.82   $227.80   $227.80  
  Purchase #7 $135.60   7.531%   $145.812   $145.81   $145.80   $145.80  
  7 purchase totals = $1,153.18       $1,263.7689   $1,263.77   $1,263.75   $1,263.70