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 $55.91   11.825%   $62.5214   $62.52   $62.50   $62.50  
  Purchase #2 $86.55   10.601%   $95.7252   $95.73   $95.75   $95.70  
  Purchase #3 $155.53   6.724%   $165.9878   $165.99   $166.00   $166.00  
  Purchase #4 $183.72   6.652%   $195.9411   $195.94   $195.95   $195.90  
  Purchase #5 $190.74   6.252%   $202.6651   $202.67   $202.65   $202.70  
  Purchase #6 $75.94   8.615%   $82.4822   $82.48   $82.50   $82.50  
  Purchase #7 $177.40   4.298%   $185.0247   $185.02   $185.00   $185.00  
  7 purchase totals = $925.79       $990.3475   $990.35   $990.35   $990.30