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 $120.27   4.211%   $125.3346   $125.33   $125.35   $125.30  
  Purchase #2 $113.94   4.438%   $118.9967   $119.00   $119.00   $119.00  
  Purchase #3 $25.76   12.543%   $28.9911   $28.99   $29.00   $29.00  
  Purchase #4 $173.48   8.152%   $187.6221   $187.62   $187.60   $187.60  
  Purchase #5 $131.61   4.771%   $137.8891   $137.89   $137.90   $137.90  
  Purchase #6 $57.73   4.609%   $60.3908   $60.39   $60.40   $60.40  
  Purchase #7 $193.82   11.823%   $216.7353   $216.74   $216.75   $216.70  
  7 purchase totals = $816.61       $875.9597   $875.96   $876.00   $875.90