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 $202.57   12.506%   $227.9034   $227.90   $227.90   $227.90  
  Purchase #2 $164.42   11.639%   $183.5568   $183.56   $183.55   $183.60  
  Purchase #3 $183.86   5.223%   $193.463   $193.46   $193.45   $193.50  
  Purchase #4 $212.68   5.400%   $224.1647   $224.16   $224.15   $224.20  
  Purchase #5 $187.37   3.711%   $194.3233   $194.32   $194.30   $194.30  
  Purchase #6 $135.39   12.560%   $152.395   $152.40   $152.40   $152.40  
  Purchase #7 $238.78   8.852%   $259.9168   $259.92   $259.90   $259.90  
  7 purchase totals = $1,325.07       $1,435.7230   $1,435.72   $1,435.65   $1,435.80