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 $56.70   12.750%   $63.9293   $63.93   $63.95   $63.90  
  Purchase #2 $62.99   4.496%   $65.822   $65.82   $65.80   $65.80  
  Purchase #3 $153.64   7.197%   $164.6975   $164.70   $164.70   $164.70  
  Purchase #4 $114.50   4.643%   $119.8162   $119.82   $119.80   $119.80  
  Purchase #5 $192.94   9.464%   $211.1998   $211.20   $211.20   $211.20  
  Purchase #6 $103.79   6.238%   $110.2644   $110.26   $110.25   $110.30  
  Purchase #7 $50.73   8.659%   $55.1227   $55.12   $55.10   $55.10  
  7 purchase totals = $735.29       $790.8519   $790.85   $790.80   $790.80