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 $180.77   10.278%   $199.3495   $199.35   $199.35   $199.30  
  Purchase #2 $158.36   13.570%   $179.8495   $179.85   $179.85   $179.80  
  Purchase #3 $143.56   9.219%   $156.7948   $156.79   $156.80   $156.80  
  Purchase #4 $227.51   7.406%   $244.3594   $244.36   $244.35   $244.40  
  Purchase #5 $51.73   6.493%   $55.0888   $55.09   $55.10   $55.10  
  Purchase #6 $225.90   8.756%   $245.6798   $245.68   $245.70   $245.70  
  Purchase #7 $147.57   5.806%   $156.1379   $156.14   $156.15   $156.10  
  7 purchase totals = $1,135.40       $1,237.2597   $1,237.26   $1,237.30   $1,237.20