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 $66.86   9.614%   $73.2879   $73.29   $73.30   $73.30  
  Purchase #2 $120.75   3.692%   $125.2081   $125.21   $125.20   $125.20  
  Purchase #3 $42.32   12.581%   $47.6443   $47.64   $47.65   $47.60  
  Purchase #4 $201.76   5.668%   $213.1958   $213.20   $213.20   $213.20  
  Purchase #5 $5.95   3.712%   $6.1709   $6.17   $6.15   $6.20  
  Purchase #6 $47.57   10.670%   $52.6457   $52.65   $52.65   $52.60  
  Purchase #7 $82.76   12.276%   $92.9196   $92.92   $92.90   $92.90  
  7 purchase totals = $567.97       $611.0723   $611.08   $611.05   $611.00