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 $250.25   6.669%   $266.9392   $266.94   $266.95   $266.90  
  Purchase #2 $78.50   10.401%   $86.6648   $86.66   $86.65   $86.70  
  Purchase #3 $132.69   13.597%   $150.7319   $150.73   $150.75   $150.70  
  Purchase #4 $194.99   11.539%   $217.4899   $217.49   $217.50   $217.50  
  Purchase #5 $178.57   11.752%   $199.5555   $199.56   $199.55   $199.60  
  Purchase #6 $124.66   3.141%   $128.5756   $128.58   $128.60   $128.60  
  Purchase #7 $191.45   5.498%   $201.9759   $201.98   $202.00   $202.00  
  7 purchase totals = $1,151.11       $1,251.9328   $1,251.94   $1,252.00   $1,252.00