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 $69.94   9.786%   $76.7843   $76.78   $76.80   $76.80  
  Purchase #2 $177.40   11.358%   $197.5491   $197.55   $197.55   $197.50  
  Purchase #3 $35.31   4.261%   $36.8146   $36.81   $36.80   $36.80  
  Purchase #4 $92.33   4.263%   $96.266   $96.27   $96.25   $96.30  
  Purchase #5 $211.51   7.180%   $226.6964   $226.70   $226.70   $226.70  
  Purchase #6 $173.71   10.681%   $192.264   $192.26   $192.25   $192.30  
  Purchase #7 $248.71   7.110%   $266.3933   $266.39   $266.40   $266.40  
  7 purchase totals = $1,008.91       $1,092.7677   $1,092.76   $1,092.75   $1,092.80