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 $89.90   4.851%   $94.261   $94.26   $94.25   $94.30  
  Purchase #2 $24.81   8.286%   $26.8658   $26.87   $26.85   $26.90  
  Purchase #3 $184.33   13.323%   $208.8883   $208.89   $208.90   $208.90  
  Purchase #4 $209.72   13.243%   $237.4932   $237.49   $237.50   $237.50  
  Purchase #5 $15.68   5.428%   $16.5311   $16.53   $16.55   $16.50  
  Purchase #6 $66.55   12.241%   $74.6964   $74.70   $74.70   $74.70  
  Purchase #7 $105.33   13.309%   $119.3484   $119.35   $119.35   $119.30  
  7 purchase totals = $696.32       $778.0842   $778.09   $778.10   $778.10