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 $233.75   7.457%   $251.1807   $251.18   $251.20   $251.20  
  Purchase #2 $97.84   4.543%   $102.2849   $102.28   $102.30   $102.30  
  Purchase #3 $119.99   7.146%   $128.5645   $128.56   $128.55   $128.60  
  Purchase #4 $46.61   10.856%   $51.67   $51.67   $51.65   $51.70  
  Purchase #5 $244.86   7.384%   $262.9405   $262.94   $262.95   $262.90  
  Purchase #6 $118.89   11.265%   $132.283   $132.28   $132.30   $132.30  
  Purchase #7 $132.96   11.455%   $148.1906   $148.19   $148.20   $148.20  
  7 purchase totals = $994.90       $1,077.1142   $1,077.10   $1,077.15   $1,077.20