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 $248.97   5.538%   $262.758   $262.76   $262.75   $262.80  
  Purchase #2 $158.61   4.613%   $165.9267   $165.93   $165.95   $165.90  
  Purchase #3 $87.72   6.410%   $93.3429   $93.34   $93.35   $93.30  
  Purchase #4 $223.68   6.113%   $237.3536   $237.35   $237.35   $237.40  
  Purchase #5 $172.82   9.829%   $189.8065   $189.81   $189.80   $189.80  
  Purchase #6 $148.56   13.272%   $168.2769   $168.28   $168.30   $168.30  
  Purchase #7 $235.80   12.301%   $264.8058   $264.81   $264.80   $264.80  
  7 purchase totals = $1,276.16       $1,382.2704   $1,382.28   $1,382.30   $1,382.30