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 $130.41   8.666%   $141.7113   $141.71   $141.70   $141.70  
  Purchase #2 $227.73   5.634%   $240.5603   $240.56   $240.55   $240.60  
  Purchase #3 $61.71   6.506%   $65.7249   $65.72   $65.70   $65.70  
  Purchase #4 $91.78   7.664%   $98.814   $98.81   $98.80   $98.80  
  Purchase #5 $53.96   13.284%   $61.128   $61.13   $61.15   $61.10  
  Purchase #6 $116.30   8.546%   $126.239   $126.24   $126.25   $126.20  
  Purchase #7 $157.89   12.817%   $178.1268   $178.13   $178.15   $178.10  
  7 purchase totals = $839.78       $912.3043   $912.30   $912.30   $912.20