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 $54.69   9.697%   $59.9933   $59.99   $60.00   $60.00  
  Purchase #2 $187.44   11.447%   $208.8963   $208.90   $208.90   $208.90  
  Purchase #3 $203.94   6.419%   $217.0309   $217.03   $217.05   $217.00  
  Purchase #4 $168.67   10.805%   $186.8948   $186.89   $186.90   $186.90  
  Purchase #5 $219.50   3.344%   $226.8401   $226.84   $226.85   $226.80  
  Purchase #6 $216.97   4.368%   $226.4472   $226.45   $226.45   $226.40  
  Purchase #7 $42.65   11.672%   $47.6281   $47.63   $47.65   $47.60  
  7 purchase totals = $1,093.86       $1,173.7307   $1,173.73   $1,173.80   $1,173.60