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 $216.49   9.247%   $236.5088   $236.51   $236.50   $236.50  
  Purchase #2 $60.56   7.504%   $65.1044   $65.10   $65.10   $65.10  
  Purchase #3 $114.76   5.867%   $121.493   $121.49   $121.50   $121.50  
  Purchase #4 $107.52   7.528%   $115.6141   $115.61   $115.60   $115.60  
  Purchase #5 $209.85   9.766%   $230.344   $230.34   $230.35   $230.30  
  Purchase #6 $76.41   11.844%   $85.46   $85.46   $85.45   $85.50  
  Purchase #7 $128.96   9.753%   $141.5375   $141.54   $141.55   $141.50  
  7 purchase totals = $914.55       $996.0618   $996.05   $996.05   $996.00