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 $227.53   8.247%   $246.2944   $246.29   $246.30   $246.30  
  Purchase #2 $198.57   3.702%   $205.9211   $205.92   $205.90   $205.90  
  Purchase #3 $250.65   11.681%   $279.9284   $279.93   $279.95   $279.90  
  Purchase #4 $135.63   7.796%   $146.2037   $146.20   $146.20   $146.20  
  Purchase #5 $66.76   5.484%   $70.4211   $70.42   $70.40   $70.40  
  Purchase #6 $15.33   13.115%   $17.3405   $17.34   $17.35   $17.30  
  Purchase #7 $67.75   11.326%   $75.4234   $75.42   $75.40   $75.40  
  7 purchase totals = $962.22       $1,041.5326   $1,041.52   $1,041.50   $1,041.40