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 $204.53   10.791%   $226.6008   $226.60   $226.60   $226.60  
  Purchase #2 $165.45   12.221%   $185.6696   $185.67   $185.65   $185.70  
  Purchase #3 $219.60   13.117%   $248.4049   $248.40   $248.40   $248.40  
  Purchase #4 $29.44   3.595%   $30.4984   $30.50   $30.50   $30.50  
  Purchase #5 $245.78   5.158%   $258.4573   $258.46   $258.45   $258.50  
  Purchase #6 $146.67   5.595%   $154.8762   $154.88   $154.90   $154.90  
  Purchase #7 $148.82   8.858%   $162.0025   $162.00   $162.00   $162.00  
  7 purchase totals = $1,160.29       $1,266.5097   $1,266.51   $1,266.50   $1,266.60