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 $59.40   13.721%   $67.5503   $67.55   $67.55   $67.60  
  Purchase #2 $139.97   8.342%   $151.6463   $151.65   $151.65   $151.60  
  Purchase #3 $187.42   11.685%   $209.32   $209.32   $209.30   $209.30  
  Purchase #4 $79.87   10.513%   $88.2667   $88.27   $88.25   $88.30  
  Purchase #5 $8.62   7.205%   $9.2411   $9.24   $9.25   $9.20  
  Purchase #6 $198.83   4.368%   $207.5149   $207.51   $207.50   $207.50  
  Purchase #7 $176.65   10.331%   $194.8997   $194.90   $194.90   $194.90  
  7 purchase totals = $850.76       $928.4390   $928.44   $928.40   $928.40