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 $90.27   12.825%   $101.8471   $101.85   $101.85   $101.80  
  Purchase #2 $239.27   9.861%   $262.8644   $262.86   $262.85   $262.90  
  Purchase #3 $33.53   4.271%   $34.9621   $34.96   $34.95   $35.00  
  Purchase #4 $94.49   9.581%   $103.5431   $103.54   $103.55   $103.50  
  Purchase #5 $144.69   11.202%   $160.8982   $160.90   $160.90   $160.90  
  Purchase #6 $186.73   10.444%   $206.2321   $206.23   $206.25   $206.20  
  Purchase #7 $204.68   7.611%   $220.2582   $220.26   $220.25   $220.30  
  7 purchase totals = $993.66       $1,090.6052   $1,090.60   $1,090.60   $1,090.60