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 $61.29   12.357%   $68.8636   $68.86   $68.85   $68.90  
  Purchase #2 $222.97   10.508%   $246.3997   $246.40   $246.40   $246.40  
  Purchase #3 $62.64   9.463%   $68.5676   $68.57   $68.55   $68.60  
  Purchase #4 $76.32   6.445%   $81.2388   $81.24   $81.25   $81.20  
  Purchase #5 $228.30   7.824%   $246.1622   $246.16   $246.15   $246.20  
  Purchase #6 $90.34   5.240%   $95.0738   $95.07   $95.05   $95.10  
  Purchase #7 $59.68   12.197%   $66.9592   $66.96   $66.95   $67.00  
  7 purchase totals = $801.54       $873.2649   $873.26   $873.20   $873.40