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 $34.46   9.652%   $37.7861   $37.79   $37.80   $37.80  
  Purchase #2 $106.91   6.536%   $113.8976   $113.90   $113.90   $113.90  
  Purchase #3 $103.61   6.679%   $110.5301   $110.53   $110.55   $110.50  
  Purchase #4 $248.42   13.513%   $281.989   $281.99   $282.00   $282.00  
  Purchase #5 $105.70   5.558%   $111.5748   $111.57   $111.55   $111.60  
  Purchase #6 $40.98   7.411%   $44.017   $44.02   $44.00   $44.00  
  Purchase #7 $160.73   3.638%   $166.5774   $166.58   $166.60   $166.60  
  7 purchase totals = $800.81       $866.3720   $866.38   $866.40   $866.40