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 $66.89   8.789%   $72.769   $72.77   $72.75   $72.80  
  Purchase #2 $10.74   13.723%   $12.2139   $12.21   $12.20   $12.20  
  Purchase #3 $92.28   11.345%   $102.7492   $102.75   $102.75   $102.70  
  Purchase #4 $151.64   10.784%   $167.9929   $167.99   $168.00   $168.00  
  Purchase #5 $239.85   10.687%   $265.4828   $265.48   $265.50   $265.50  
  Purchase #6 $205.27   6.585%   $218.787   $218.79   $218.80   $218.80  
  Purchase #7 $232.91   12.848%   $262.8343   $262.83   $262.85   $262.80  
  7 purchase totals = $999.58       $1,102.8291   $1,102.82   $1,102.85   $1,102.80