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 $60.55   12.279%   $67.9849   $67.98   $68.00   $68.00  
  Purchase #2 $138.35   7.329%   $148.4897   $148.49   $148.50   $148.50  
  Purchase #3 $165.38   9.754%   $181.5112   $181.51   $181.50   $181.50  
  Purchase #4 $124.96   11.506%   $139.3379   $139.34   $139.35   $139.30  
  Purchase #5 $146.27   11.536%   $163.1437   $163.14   $163.15   $163.10  
  Purchase #6 $81.52   10.831%   $90.3494   $90.35   $90.35   $90.30  
  Purchase #7 $177.88   9.712%   $195.1557   $195.16   $195.15   $195.20  
  7 purchase totals = $894.91       $985.9725   $985.97   $986.00   $985.90