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 $86.42   13.828%   $98.3702   $98.37   $98.35   $98.40  
  Purchase #2 $183.56   12.290%   $206.1195   $206.12   $206.10   $206.10  
  Purchase #3 $239.83   11.454%   $267.3001   $267.30   $267.30   $267.30  
  Purchase #4 $100.57   12.522%   $113.1634   $113.16   $113.15   $113.20  
  Purchase #5 $22.52   8.143%   $24.3538   $24.35   $24.35   $24.40  
  Purchase #6 $53.30   4.851%   $55.8856   $55.89   $55.90   $55.90  
  Purchase #7 $214.99   3.859%   $223.2865   $223.29   $223.30   $223.30  
  7 purchase totals = $901.19       $988.4791   $988.48   $988.45   $988.60