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 $65.37   8.127%   $70.6826   $70.68   $70.70   $70.70  
  Purchase #2 $47.78   3.872%   $49.63   $49.63   $49.65   $49.60  
  Purchase #3 $58.73   9.566%   $64.3481   $64.35   $64.35   $64.30  
  Purchase #4 $164.91   6.498%   $175.6259   $175.63   $175.65   $175.60  
  Purchase #5 $173.47   6.540%   $184.8149   $184.81   $184.80   $184.80  
  Purchase #6 $32.33   7.325%   $34.6982   $34.70   $34.70   $34.70  
  Purchase #7 $170.35   12.555%   $191.7374   $191.74   $191.75   $191.70  
  7 purchase totals = $712.94       $771.5371   $771.54   $771.60   $771.40