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 $180.60   10.164%   $198.9562   $198.96   $198.95   $199.00  
  Purchase #2 $24.36   12.182%   $27.3275   $27.33   $27.35   $27.30  
  Purchase #3 $101.64   10.735%   $112.5511   $112.55   $112.55   $112.60  
  Purchase #4 $235.28   11.272%   $261.8008   $261.80   $261.80   $261.80  
  Purchase #5 $163.29   10.707%   $180.7735   $180.77   $180.75   $180.80  
  Purchase #6 $50.49   12.820%   $56.9628   $56.96   $56.95   $57.00  
  Purchase #7 $212.97   9.788%   $233.8155   $233.82   $233.80   $233.80  
  7 purchase totals = $968.63       $1,072.1874   $1,072.19   $1,072.15   $1,072.30