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 $63.63   8.581%   $69.0901   $69.09   $69.10   $69.10  
  Purchase #2 $163.88   8.745%   $178.2113   $178.21   $178.20   $178.20  
  Purchase #3 $25.70   10.844%   $28.4869   $28.49   $28.50   $28.50  
  Purchase #4 $142.45   13.793%   $162.0981   $162.10   $162.10   $162.10  
  Purchase #5 $233.96   8.217%   $253.1845   $253.18   $253.20   $253.20  
  Purchase #6 $227.68   4.672%   $238.3172   $238.32   $238.30   $238.30  
  Purchase #7 $127.82   6.579%   $136.2293   $136.23   $136.25   $136.20  
  7 purchase totals = $985.12       $1,065.6174   $1,065.62   $1,065.65   $1,065.60