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 $205.67   10.460%   $227.1831   $227.18   $227.20   $227.20  
  Purchase #2 $53.34   8.677%   $57.9683   $57.97   $57.95   $58.00  
  Purchase #3 $154.40   5.677%   $163.1653   $163.17   $163.15   $163.20  
  Purchase #4 $194.55   10.213%   $214.4194   $214.42   $214.40   $214.40  
  Purchase #5 $132.71   8.679%   $144.2279   $144.23   $144.25   $144.20  
  Purchase #6 $112.29   10.562%   $124.1501   $124.15   $124.15   $124.20  
  Purchase #7 $127.74   3.376%   $132.0525   $132.05   $132.05   $132.10  
  7 purchase totals = $980.70       $1,063.1666   $1,063.17   $1,063.15   $1,063.30