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 $245.63   5.544%   $259.2477   $259.25   $259.25   $259.20  
  Purchase #2 $250.62   10.379%   $276.6318   $276.63   $276.65   $276.60  
  Purchase #3 $238.92   8.419%   $259.0347   $259.03   $259.05   $259.00  
  Purchase #4 $150.60   13.456%   $170.8647   $170.86   $170.85   $170.90  
  Purchase #5 $210.73   5.335%   $221.9724   $221.97   $221.95   $222.00  
  Purchase #6 $216.48   11.593%   $241.5765   $241.58   $241.60   $241.60  
  Purchase #7 $14.66   12.327%   $16.4671   $16.47   $16.45   $16.50  
  7 purchase totals = $1,327.64       $1,445.7949   $1,445.79   $1,445.80   $1,445.80