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 $227.85   8.202%   $246.5383   $246.54   $246.55   $246.50  
  Purchase #2 $101.41   6.296%   $107.7948   $107.79   $107.80   $107.80  
  Purchase #3 $192.31   12.499%   $216.3468   $216.35   $216.35   $216.30  
  Purchase #4 $153.50   8.248%   $166.1607   $166.16   $166.15   $166.20  
  Purchase #5 $94.55   9.648%   $103.6722   $103.67   $103.65   $103.70  
  Purchase #6 $159.30   12.522%   $179.2475   $179.25   $179.25   $179.20  
  Purchase #7 $71.40   7.189%   $76.5329   $76.53   $76.55   $76.50  
  7 purchase totals = $1,000.32       $1,096.2932   $1,096.29   $1,096.30   $1,096.20