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 $61.66   12.390%   $69.2997   $69.30   $69.30   $69.30  
  Purchase #2 $214.33   3.856%   $222.5946   $222.59   $222.60   $222.60  
  Purchase #3 $189.46   12.137%   $212.4548   $212.45   $212.45   $212.50  
  Purchase #4 $125.27   11.286%   $139.408   $139.41   $139.40   $139.40  
  Purchase #5 $126.42   11.814%   $141.3553   $141.36   $141.35   $141.40  
  Purchase #6 $68.40   3.761%   $70.9725   $70.97   $70.95   $71.00  
  Purchase #7 $126.87   10.778%   $140.544   $140.54   $140.55   $140.50  
  7 purchase totals = $912.41       $996.6289   $996.62   $996.60   $996.70