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 $10.63   12.427%   $11.951   $11.95   $11.95   $12.00  
  Purchase #2 $158.55   11.332%   $176.5169   $176.52   $176.50   $176.50  
  Purchase #3 $119.70   5.594%   $126.396   $126.40   $126.40   $126.40  
  Purchase #4 $174.46   9.677%   $191.3425   $191.34   $191.35   $191.30  
  Purchase #5 $91.71   5.691%   $96.9292   $96.93   $96.95   $96.90  
  Purchase #6 $8.29   11.388%   $9.2341   $9.23   $9.25   $9.20  
  Purchase #7 $156.88   3.534%   $162.4241   $162.42   $162.40   $162.40  
  7 purchase totals = $720.22       $774.7938   $774.79   $774.80   $774.70