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 $107.98   13.532%   $122.5919   $122.59   $122.60   $122.60  
  Purchase #2 $226.55   11.235%   $252.0029   $252.00   $252.00   $252.00  
  Purchase #3 $24.51   4.531%   $25.6205   $25.62   $25.60   $25.60  
  Purchase #4 $34.86   13.450%   $39.5487   $39.55   $39.55   $39.50  
  Purchase #5 $213.98   9.574%   $234.4664   $234.47   $234.45   $234.50  
  Purchase #6 $23.37   12.111%   $26.2003   $26.20   $26.20   $26.20  
  Purchase #7 $153.53   5.593%   $162.1169   $162.12   $162.10   $162.10  
  7 purchase totals = $784.78       $862.5476   $862.55   $862.50   $862.50