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 $216.36   10.442%   $238.9523   $238.95   $238.95   $239.00  
  Purchase #2 $244.72   7.284%   $262.5454   $262.55   $262.55   $262.50  
  Purchase #3 $36.63   12.244%   $41.115   $41.12   $41.10   $41.10  
  Purchase #4 $61.62   9.484%   $67.464   $67.46   $67.45   $67.50  
  Purchase #5 $243.63   9.652%   $267.1452   $267.15   $267.15   $267.10  
  Purchase #6 $170.62   3.481%   $176.5593   $176.56   $176.55   $176.60  
  Purchase #7 $218.36   8.408%   $236.7197   $236.72   $236.70   $236.70  
  7 purchase totals = $1,191.94       $1,290.5009   $1,290.51   $1,290.45   $1,290.50