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 $115.63   7.222%   $123.9808   $123.98   $124.00   $124.00  
  Purchase #2 $184.43   3.509%   $190.9016   $190.90   $190.90   $190.90  
  Purchase #3 $81.71   11.361%   $90.9931   $90.99   $91.00   $91.00  
  Purchase #4 $22.52   13.527%   $25.5663   $25.57   $25.55   $25.60  
  Purchase #5 $91.37   4.421%   $95.4095   $95.41   $95.40   $95.40  
  Purchase #6 $67.97   4.409%   $70.9668   $70.97   $70.95   $71.00  
  Purchase #7 $162.73   3.202%   $167.9406   $167.94   $167.95   $167.90  
  7 purchase totals = $726.36       $765.7587   $765.76   $765.75   $765.80