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 $56.64   8.372%   $61.3819   $61.38   $61.40   $61.40  
  Purchase #2 $127.25   10.364%   $140.4382   $140.44   $140.45   $140.40  
  Purchase #3 $210.43   12.612%   $236.9694   $236.97   $236.95   $237.00  
  Purchase #4 $215.51   13.151%   $243.8517   $243.85   $243.85   $243.90  
  Purchase #5 $182.73   9.865%   $200.7563   $200.76   $200.75   $200.80  
  Purchase #6 $211.81   10.151%   $233.3108   $233.31   $233.30   $233.30  
  Purchase #7 $226.31   4.667%   $236.8719   $236.87   $236.85   $236.90  
  7 purchase totals = $1,230.68       $1,353.5802   $1,353.58   $1,353.55   $1,353.70