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 $61.57   10.818%   $68.2306   $68.23   $68.25   $68.20  
  Purchase #2 $162.76   12.181%   $182.5858   $182.59   $182.60   $182.60  
  Purchase #3 $85.61   12.865%   $96.6237   $96.62   $96.60   $96.60  
  Purchase #4 $8.81   3.851%   $9.1493   $9.15   $9.15   $9.10  
  Purchase #5 $67.66   10.823%   $74.9828   $74.98   $75.00   $75.00  
  Purchase #6 $127.71   6.825%   $136.4262   $136.43   $136.45   $136.40  
  Purchase #7 $196.91   10.350%   $217.2902   $217.29   $217.30   $217.30  
  7 purchase totals = $711.03       $785.2886   $785.29   $785.35   $785.20