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 $112.84   11.249%   $125.5334   $125.53   $125.55   $125.50  
  Purchase #2 $248.80   10.720%   $275.4714   $275.47   $275.45   $275.50  
  Purchase #3 $60.44   4.782%   $63.3302   $63.33   $63.35   $63.30  
  Purchase #4 $132.29   7.230%   $141.8546   $141.85   $141.85   $141.90  
  Purchase #5 $194.34   5.644%   $205.3085   $205.31   $205.30   $205.30  
  Purchase #6 $164.93   11.680%   $184.1938   $184.19   $184.20   $184.20  
  Purchase #7 $78.60   10.203%   $86.6196   $86.62   $86.60   $86.60  
  7 purchase totals = $992.24       $1,082.3115   $1,082.30   $1,082.30   $1,082.30