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 $136.49   11.527%   $152.2232   $152.22   $152.20   $152.20  
  Purchase #2 $182.84   5.582%   $193.0461   $193.05   $193.05   $193.00  
  Purchase #3 $87.58   5.501%   $92.3978   $92.40   $92.40   $92.40  
  Purchase #4 $203.63   7.289%   $218.4726   $218.47   $218.45   $218.50  
  Purchase #5 $122.58   8.584%   $133.1023   $133.10   $133.10   $133.10  
  Purchase #6 $236.49   3.392%   $244.5117   $244.51   $244.50   $244.50  
  Purchase #7 $159.34   6.646%   $169.9297   $169.93   $169.95   $169.90  
  7 purchase totals = $1,128.95       $1,203.6834   $1,203.68   $1,203.65   $1,203.60