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 $62.80   9.391%   $68.6975   $68.70   $68.70   $68.70  
  Purchase #2 $191.51   8.296%   $207.3977   $207.40   $207.40   $207.40  
  Purchase #3 $164.48   7.217%   $176.3505   $176.35   $176.35   $176.40  
  Purchase #4 $140.79   5.140%   $148.0266   $148.03   $148.05   $148.00  
  Purchase #5 $30.50   10.678%   $33.7568   $33.76   $33.75   $33.80  
  Purchase #6 $14.84   8.252%   $16.0646   $16.06   $16.05   $16.10  
  Purchase #7 $56.41   4.289%   $58.8294   $58.83   $58.85   $58.80  
  7 purchase totals = $661.33       $709.1231   $709.13   $709.15   $709.20