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 $226.38   10.677%   $250.5506   $250.55   $250.55   $250.60  
  Purchase #2 $239.63   13.357%   $271.6374   $271.64   $271.65   $271.60  
  Purchase #3 $227.36   13.403%   $257.8331   $257.83   $257.85   $257.80  
  Purchase #4 $238.43   4.471%   $249.0902   $249.09   $249.10   $249.10  
  Purchase #5 $133.90   9.844%   $147.0811   $147.08   $147.10   $147.10  
  Purchase #6 $157.32   9.294%   $171.9413   $171.94   $171.95   $171.90  
  Purchase #7 $63.93   7.523%   $68.7395   $68.74   $68.75   $68.70  
  7 purchase totals = $1,286.95       $1,416.8732   $1,416.87   $1,416.95   $1,416.80