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 $166.79   4.316%   $173.9887   $173.99   $174.00   $174.00  
  Purchase #2 $32.54   8.503%   $35.3069   $35.31   $35.30   $35.30  
  Purchase #3 $74.30   11.655%   $82.9597   $82.96   $82.95   $83.00  
  Purchase #4 $233.72   11.862%   $261.4439   $261.44   $261.45   $261.40  
  Purchase #5 $11.29   12.410%   $12.6911   $12.69   $12.70   $12.70  
  Purchase #6 $220.38   6.420%   $234.5284   $234.53   $234.55   $234.50  
  Purchase #7 $81.74   3.716%   $84.7775   $84.78   $84.80   $84.80  
  7 purchase totals = $820.76       $885.6962   $885.70   $885.75   $885.70