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 $192.90   8.373%   $209.0515   $209.05   $209.05   $209.10  
  Purchase #2 $64.94   6.160%   $68.9403   $68.94   $68.95   $68.90  
  Purchase #3 $61.54   3.739%   $63.841   $63.84   $63.85   $63.80  
  Purchase #4 $63.39   13.784%   $72.1277   $72.13   $72.15   $72.10  
  Purchase #5 $249.51   9.295%   $272.702   $272.70   $272.70   $272.70  
  Purchase #6 $50.92   9.442%   $55.7279   $55.73   $55.75   $55.70  
  Purchase #7 $199.59   11.702%   $222.946   $222.95   $222.95   $222.90  
  7 purchase totals = $882.79       $965.3364   $965.34   $965.40   $965.20