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 $58.38   3.289%   $60.3001   $60.30   $60.30   $60.30  
  Purchase #2 $235.49   13.162%   $266.4852   $266.49   $266.50   $266.50  
  Purchase #3 $187.29   10.245%   $206.4779   $206.48   $206.50   $206.50  
  Purchase #4 $173.82   5.819%   $183.9346   $183.93   $183.95   $183.90  
  Purchase #5 $93.49   12.294%   $104.9837   $104.98   $105.00   $105.00  
  Purchase #6 $58.53   13.445%   $66.3994   $66.40   $66.40   $66.40  
  Purchase #7 $70.44   3.631%   $72.9977   $73.00   $73.00   $73.00  
  7 purchase totals = $877.44       $961.5786   $961.58   $961.65   $961.60