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 $147.58   9.778%   $162.0104   $162.01   $162.00   $162.00  
  Purchase #2 $249.69   8.794%   $271.6477   $271.65   $271.65   $271.60  
  Purchase #3 $65.99   8.360%   $71.5068   $71.51   $71.50   $71.50  
  Purchase #4 $57.52   5.144%   $60.4788   $60.48   $60.50   $60.50  
  Purchase #5 $109.39   10.526%   $120.9044   $120.90   $120.90   $120.90  
  Purchase #6 $114.99   13.222%   $130.194   $130.19   $130.20   $130.20  
  Purchase #7 $48.90   3.272%   $50.5   $50.50   $50.50   $50.50  
  7 purchase totals = $794.06       $867.2421   $867.24   $867.25   $867.20