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 $92.61   13.613%   $105.217   $105.22   $105.20   $105.20  
  Purchase #2 $14.43   7.442%   $15.5039   $15.50   $15.50   $15.50  
  Purchase #3 $116.98   10.245%   $128.9646   $128.96   $128.95   $129.00  
  Purchase #4 $79.74   7.369%   $85.616   $85.62   $85.60   $85.60  
  Purchase #5 $176.85   4.317%   $184.4846   $184.48   $184.50   $184.50  
  Purchase #6 $245.64   5.508%   $259.1699   $259.17   $259.15   $259.20  
  Purchase #7 $150.39   11.704%   $167.9916   $167.99   $168.00   $168.00  
  7 purchase totals = $876.64       $946.9476   $946.94   $946.90   $947.00