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 $147.46   6.482%   $157.0184   $157.02   $157.00   $157.00  
  Purchase #2 $95.67   8.581%   $103.8794   $103.88   $103.90   $103.90  
  Purchase #3 $214.51   11.870%   $239.9723   $239.97   $239.95   $240.00  
  Purchase #4 $104.87   11.329%   $116.7507   $116.75   $116.75   $116.80  
  Purchase #5 $247.64   5.736%   $261.8446   $261.84   $261.85   $261.80  
  Purchase #6 $68.30   3.243%   $70.515   $70.52   $70.50   $70.50  
  Purchase #7 $153.42   9.220%   $167.5653   $167.57   $167.55   $167.60  
  7 purchase totals = $1,031.87       $1,117.5457   $1,117.55   $1,117.50   $1,117.60