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 $92.34   10.707%   $102.2268   $102.23   $102.25   $102.20  
  Purchase #2 $63.37   4.560%   $66.2597   $66.26   $66.25   $66.30  
  Purchase #3 $150.61   11.130%   $167.3729   $167.37   $167.35   $167.40  
  Purchase #4 $113.60   13.772%   $129.245   $129.25   $129.25   $129.20  
  Purchase #5 $49.80   6.658%   $53.1157   $53.12   $53.10   $53.10  
  Purchase #6 $76.76   6.409%   $81.6795   $81.68   $81.70   $81.70  
  Purchase #7 $30.70   4.133%   $31.9688   $31.97   $31.95   $32.00  
  7 purchase totals = $577.18       $631.8684   $631.88   $631.85   $631.90