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 $168.88   4.772%   $176.939   $176.94   $176.95   $176.90  
  Purchase #2 $248.48   7.655%   $267.5011   $267.50   $267.50   $267.50  
  Purchase #3 $148.32   11.796%   $165.8158   $165.82   $165.80   $165.80  
  Purchase #4 $197.86   3.578%   $204.9394   $204.94   $204.95   $204.90  
  Purchase #5 $227.51   4.580%   $237.93   $237.93   $237.95   $237.90  
  Purchase #6 $53.78   5.289%   $56.6244   $56.62   $56.60   $56.60  
  Purchase #7 $231.29   11.383%   $257.6177   $257.62   $257.60   $257.60  
  7 purchase totals = $1,276.12       $1,367.3674   $1,367.37   $1,367.35   $1,367.20