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 $86.59   12.306%   $97.2458   $97.25   $97.25   $97.20  
  Purchase #2 $95.62   3.505%   $98.9715   $98.97   $98.95   $99.00  
  Purchase #3 $118.65   5.352%   $125.0001   $125.00   $125.00   $125.00  
  Purchase #4 $7.80   9.444%   $8.5366   $8.54   $8.55   $8.50  
  Purchase #5 $165.64   11.144%   $184.0989   $184.10   $184.10   $184.10  
  Purchase #6 $89.99   11.197%   $100.0662   $100.07   $100.05   $100.10  
  Purchase #7 $68.47   11.403%   $76.2776   $76.28   $76.30   $76.30  
  7 purchase totals = $632.76       $690.1967   $690.21   $690.20   $690.20