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 $91.59   6.206%   $97.2741   $97.27   $97.25   $97.30  
  Purchase #2 $102.90   3.815%   $106.8256   $106.83   $106.85   $106.80  
  Purchase #3 $232.78   13.428%   $264.0377   $264.04   $264.05   $264.00  
  Purchase #4 $137.77   7.134%   $147.5985   $147.60   $147.60   $147.60  
  Purchase #5 $114.83   5.784%   $121.4718   $121.47   $121.45   $121.50  
  Purchase #6 $154.99   8.866%   $168.7314   $168.73   $168.75   $168.70  
  Purchase #7 $46.44   5.455%   $48.9733   $48.97   $48.95   $49.00  
  7 purchase totals = $881.30       $954.9124   $954.91   $954.90   $954.90