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 $248.49   13.486%   $282.0014   $282.00   $282.00   $282.00  
  Purchase #2 $167.53   5.487%   $176.7224   $176.72   $176.70   $176.70  
  Purchase #3 $166.98   13.161%   $188.9562   $188.96   $188.95   $189.00  
  Purchase #4 $81.70   8.342%   $88.5154   $88.52   $88.50   $88.50  
  Purchase #5 $230.76   5.267%   $242.9141   $242.91   $242.90   $242.90  
  Purchase #6 $247.69   8.847%   $269.6031   $269.60   $269.60   $269.60  
  Purchase #7 $229.74   5.510%   $242.3987   $242.40   $242.40   $242.40  
  7 purchase totals = $1,372.89       $1,491.1113   $1,491.11   $1,491.05   $1,491.10