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 $240.82   11.702%   $269.0008   $269.00   $269.00   $269.00  
  Purchase #2 $11.32   9.643%   $12.4116   $12.41   $12.40   $12.40  
  Purchase #3 $245.53   5.347%   $258.6585   $258.66   $258.65   $258.70  
  Purchase #4 $236.59   13.219%   $267.8648   $267.86   $267.85   $267.90  
  Purchase #5 $34.82   9.491%   $38.1248   $38.12   $38.10   $38.10  
  Purchase #6 $119.63   9.567%   $131.075   $131.08   $131.10   $131.10  
  Purchase #7 $125.37   11.700%   $140.0383   $140.04   $140.05   $140.00  
  7 purchase totals = $1,014.08       $1,117.1738   $1,117.17   $1,117.15   $1,117.20