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 $24.46   5.210%   $25.7344   $25.73   $25.75   $25.70  
  Purchase #2 $92.78   8.530%   $100.6941   $100.69   $100.70   $100.70  
  Purchase #3 $118.56   7.516%   $127.471   $127.47   $127.45   $127.50  
  Purchase #4 $113.96   9.180%   $124.4215   $124.42   $124.40   $124.40  
  Purchase #5 $77.67   4.291%   $81.0028   $81.00   $81.00   $81.00  
  Purchase #6 $219.97   7.678%   $236.8593   $236.86   $236.85   $236.90  
  Purchase #7 $207.86   9.531%   $227.6711   $227.67   $227.65   $227.70  
  7 purchase totals = $855.26       $923.8542   $923.84   $923.80   $923.90