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 $49.70   6.778%   $53.0687   $53.07   $53.05   $53.10  
  Purchase #2 $232.98   11.813%   $260.5019   $260.50   $260.50   $260.50  
  Purchase #3 $85.31   5.675%   $90.1513   $90.15   $90.15   $90.20  
  Purchase #4 $172.98   11.551%   $192.9609   $192.96   $192.95   $193.00  
  Purchase #5 $167.74   6.273%   $178.2623   $178.26   $178.25   $178.30  
  Purchase #6 $22.98   3.409%   $23.7634   $23.76   $23.75   $23.80  
  Purchase #7 $166.38   12.550%   $187.2607   $187.26   $187.25   $187.30  
  7 purchase totals = $898.07       $985.9692   $985.96   $985.90   $986.20