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 $31.49   9.658%   $34.5313   $34.53   $34.55   $34.50  
  Purchase #2 $177.34   8.622%   $192.6303   $192.63   $192.65   $192.60  
  Purchase #3 $8.57   12.817%   $9.6684   $9.67   $9.65   $9.70  
  Purchase #4 $115.87   6.481%   $123.3795   $123.38   $123.40   $123.40  
  Purchase #5 $37.42   9.706%   $41.052   $41.05   $41.05   $41.10  
  Purchase #6 $214.43   8.587%   $232.8431   $232.84   $232.85   $232.80  
  Purchase #7 $143.63   12.242%   $161.2132   $161.21   $161.20   $161.20  
  7 purchase totals = $728.75       $795.3178   $795.31   $795.35   $795.30