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 $159.40   12.808%   $179.816   $179.82   $179.80   $179.80  
  Purchase #2 $248.50   9.367%   $271.777   $271.78   $271.80   $271.80  
  Purchase #3 $61.51   7.300%   $66.0002   $66.00   $66.00   $66.00  
  Purchase #4 $47.86   8.204%   $51.7864   $51.79   $51.80   $51.80  
  Purchase #5 $176.26   13.182%   $199.4946   $199.49   $199.50   $199.50  
  Purchase #6 $225.33   4.572%   $235.6321   $235.63   $235.65   $235.60  
  Purchase #7 $79.83   12.408%   $89.7353   $89.74   $89.75   $89.70  
  7 purchase totals = $998.69       $1,094.2416   $1,094.25   $1,094.30   $1,094.20