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 $53.71   9.312%   $58.7115   $58.71   $58.70   $58.70  
  Purchase #2 $146.97   6.114%   $155.9557   $155.96   $155.95   $156.00  
  Purchase #3 $58.77   8.106%   $63.5339   $63.53   $63.55   $63.50  
  Purchase #4 $136.72   13.524%   $155.21   $155.21   $155.20   $155.20  
  Purchase #5 $32.51   6.722%   $34.6953   $34.70   $34.70   $34.70  
  Purchase #6 $127.72   12.274%   $143.3964   $143.40   $143.40   $143.40  
  Purchase #7 $196.99   3.722%   $204.322   $204.32   $204.30   $204.30  
  7 purchase totals = $753.39       $815.8248   $815.83   $815.80   $815.80