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 $223.93   13.143%   $253.3611   $253.36   $253.35   $253.40  
  Purchase #2 $175.29   11.582%   $195.5921   $195.59   $195.60   $195.60  
  Purchase #3 $177.74   8.145%   $192.2169   $192.22   $192.20   $192.20  
  Purchase #4 $148.68   10.307%   $164.0044   $164.00   $164.00   $164.00  
  Purchase #5 $194.30   9.786%   $213.3142   $213.31   $213.30   $213.30  
  Purchase #6 $199.71   8.612%   $216.909   $216.91   $216.90   $216.90  
  Purchase #7 $156.60   5.434%   $165.1096   $165.11   $165.10   $165.10  
  7 purchase totals = $1,276.25       $1,400.5073   $1,400.50   $1,400.45   $1,400.50