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 $137.50   8.174%   $148.7393   $148.74   $148.75   $148.70  
  Purchase #2 $250.51   4.726%   $262.3491   $262.35   $262.35   $262.30  
  Purchase #3 $172.87   4.285%   $180.2775   $180.28   $180.30   $180.30  
  Purchase #4 $21.43   10.742%   $23.732   $23.73   $23.75   $23.70  
  Purchase #5 $77.97   5.616%   $82.3488   $82.35   $82.35   $82.30  
  Purchase #6 $243.91   3.829%   $253.2493   $253.25   $253.25   $253.20  
  Purchase #7 $135.34   5.295%   $142.5063   $142.51   $142.50   $142.50  
  7 purchase totals = $1,039.53       $1,093.2023   $1,093.21   $1,093.25   $1,093.00