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 $68.38   10.747%   $75.7288   $75.73   $75.75   $75.70  
  Purchase #2 $60.39   9.378%   $66.0534   $66.05   $66.05   $66.10  
  Purchase #3 $91.75   11.424%   $102.2315   $102.23   $102.25   $102.20  
  Purchase #4 $116.31   4.683%   $121.7568   $121.76   $121.75   $121.80  
  Purchase #5 $98.70   6.649%   $105.2626   $105.26   $105.25   $105.30  
  Purchase #6 $192.51   6.775%   $205.5526   $205.55   $205.55   $205.60  
  Purchase #7 $42.96   10.695%   $47.5546   $47.55   $47.55   $47.60  
  7 purchase totals = $671.00       $724.1403   $724.13   $724.15   $724.30