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 $29.92   11.284%   $33.2962   $33.30   $33.30   $33.30  
  Purchase #2 $61.95   6.540%   $66.0015   $66.00   $66.00   $66.00  
  Purchase #3 $247.29   13.783%   $281.374   $281.37   $281.35   $281.40  
  Purchase #4 $84.74   8.564%   $91.9971   $92.00   $92.00   $92.00  
  Purchase #5 $139.35   7.785%   $150.1984   $150.20   $150.20   $150.20  
  Purchase #6 $65.27   3.227%   $67.3763   $67.38   $67.40   $67.40  
  Purchase #7 $67.77   9.491%   $74.2021   $74.20   $74.20   $74.20  
  7 purchase totals = $696.29       $764.4456   $764.45   $764.45   $764.50