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 $214.81   10.313%   $236.9634   $236.96   $236.95   $237.00  
  Purchase #2 $63.82   6.534%   $67.99   $67.99   $68.00   $68.00  
  Purchase #3 $205.70   5.350%   $216.705   $216.71   $216.70   $216.70  
  Purchase #4 $238.90   13.806%   $271.8825   $271.88   $271.90   $271.90  
  Purchase #5 $135.75   5.727%   $143.5244   $143.52   $143.50   $143.50  
  Purchase #6 $153.69   3.565%   $159.169   $159.17   $159.15   $159.20  
  Purchase #7 $109.81   8.506%   $119.1504   $119.15   $119.15   $119.20  
  7 purchase totals = $1,122.48       $1,215.3847   $1,215.38   $1,215.35   $1,215.50