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 $28.86   11.753%   $32.2519   $32.25   $32.25   $32.30  
  Purchase #2 $128.31   3.135%   $132.3325   $132.33   $132.35   $132.30  
  Purchase #3 $199.59   7.179%   $213.9186   $213.92   $213.90   $213.90  
  Purchase #4 $198.93   4.858%   $208.594   $208.59   $208.60   $208.60  
  Purchase #5 $143.66   13.706%   $163.35   $163.35   $163.35   $163.40  
  Purchase #6 $233.42   11.151%   $259.4487   $259.45   $259.45   $259.40  
  Purchase #7 $166.75   10.649%   $184.5072   $184.51   $184.50   $184.50  
  7 purchase totals = $1,099.52       $1,194.4029   $1,194.40   $1,194.40   $1,194.40