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 $126.76   11.734%   $141.634   $141.63   $141.65   $141.60  
  Purchase #2 $152.78   7.113%   $163.6472   $163.65   $163.65   $163.60  
  Purchase #3 $116.54   8.662%   $126.6347   $126.63   $126.65   $126.60  
  Purchase #4 $219.61   13.307%   $248.8335   $248.83   $248.85   $248.80  
  Purchase #5 $97.28   6.575%   $103.6762   $103.68   $103.70   $103.70  
  Purchase #6 $171.63   11.155%   $190.7753   $190.78   $190.80   $190.80  
  Purchase #7 $44.33   4.858%   $46.4836   $46.48   $46.50   $46.50  
  7 purchase totals = $928.93       $1,021.6845   $1,021.68   $1,021.80   $1,021.60