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 $88.97   7.536%   $95.6748   $95.67   $95.65   $95.70  
  Purchase #2 $46.59   9.372%   $50.9564   $50.96   $50.95   $51.00  
  Purchase #3 $209.78   7.165%   $224.8107   $224.81   $224.80   $224.80  
  Purchase #4 $166.82   11.136%   $185.3971   $185.40   $185.40   $185.40  
  Purchase #5 $192.41   8.856%   $209.4498   $209.45   $209.45   $209.40  
  Purchase #6 $63.48   13.590%   $72.1069   $72.11   $72.10   $72.10  
  Purchase #7 $137.96   3.534%   $142.8355   $142.84   $142.85   $142.80  
  7 purchase totals = $906.01       $981.2312   $981.24   $981.20   $981.20