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 $82.88   4.593%   $86.6867   $86.69   $86.70   $86.70  
  Purchase #2 $178.48   7.201%   $191.3323   $191.33   $191.35   $191.30  
  Purchase #3 $151.74   9.856%   $166.6955   $166.70   $166.70   $166.70  
  Purchase #4 $214.36   6.254%   $227.7661   $227.77   $227.75   $227.80  
  Purchase #5 $206.91   12.461%   $232.6931   $232.69   $232.70   $232.70  
  Purchase #6 $75.35   11.484%   $84.0032   $84.00   $84.00   $84.00  
  Purchase #7 $231.79   5.448%   $244.4179   $244.42   $244.40   $244.40  
  7 purchase totals = $1,141.51       $1,233.5948   $1,233.60   $1,233.60   $1,233.60