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 $31.41   10.855%   $34.8196   $34.82   $34.80   $34.80  
  Purchase #2 $95.32   12.296%   $107.0405   $107.04   $107.05   $107.00  
  Purchase #3 $118.76   7.227%   $127.3428   $127.34   $127.35   $127.30  
  Purchase #4 $182.63   9.480%   $199.9433   $199.94   $199.95   $199.90  
  Purchase #5 $61.97   5.651%   $65.4719   $65.47   $65.45   $65.50  
  Purchase #6 $191.34   5.590%   $202.0359   $202.04   $202.05   $202.00  
  Purchase #7 $114.60   3.199%   $118.2661   $118.27   $118.25   $118.30  
  7 purchase totals = $796.03       $854.9201   $854.92   $854.90   $854.80