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 $45.34   7.659%   $48.8126   $48.81   $48.80   $48.80  
  Purchase #2 $158.58   10.576%   $175.3514   $175.35   $175.35   $175.40  
  Purchase #3 $30.80   6.719%   $32.8695   $32.87   $32.85   $32.90  
  Purchase #4 $187.91   6.388%   $199.9137   $199.91   $199.90   $199.90  
  Purchase #5 $25.53   9.749%   $28.0189   $28.02   $28.00   $28.00  
  Purchase #6 $176.53   7.857%   $190.4   $190.40   $190.40   $190.40  
  Purchase #7 $76.89   10.209%   $84.7397   $84.74   $84.75   $84.70  
  7 purchase totals = $701.58       $760.1058   $760.10   $760.05   $760.10