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 $119.82   5.495%   $126.4041   $126.40   $126.40   $126.40  
  Purchase #2 $148.35   12.437%   $166.8003   $166.80   $166.80   $166.80  
  Purchase #3 $208.76   7.466%   $224.346   $224.35   $224.35   $224.30  
  Purchase #4 $239.67   3.338%   $247.6702   $247.67   $247.65   $247.70  
  Purchase #5 $179.88   11.169%   $199.9708   $199.97   $199.95   $200.00  
  Purchase #6 $167.29   9.247%   $182.7593   $182.76   $182.75   $182.80  
  Purchase #7 $90.51   10.203%   $99.7447   $99.74   $99.75   $99.70  
  7 purchase totals = $1,154.28       $1,247.6954   $1,247.69   $1,247.65   $1,247.70