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 $206.31   10.181%   $227.3144   $227.31   $227.30   $227.30  
  Purchase #2 $61.34   7.505%   $65.9436   $65.94   $65.95   $65.90  
  Purchase #3 $23.70   13.651%   $26.9353   $26.94   $26.95   $26.90  
  Purchase #4 $157.45   3.770%   $163.3859   $163.39   $163.40   $163.40  
  Purchase #5 $89.43   8.111%   $96.6837   $96.68   $96.70   $96.70  
  Purchase #6 $232.75   7.858%   $251.0395   $251.04   $251.05   $251.00  
  Purchase #7 $103.99   9.643%   $114.0178   $114.02   $114.00   $114.00  
  7 purchase totals = $874.97       $945.3202   $945.32   $945.35   $945.20