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 $94.76   6.857%   $101.2577   $101.26   $101.25   $101.30  
  Purchase #2 $171.47   4.253%   $178.7626   $178.76   $178.75   $178.80  
  Purchase #3 $210.25   5.172%   $221.1241   $221.12   $221.10   $221.10  
  Purchase #4 $80.71   7.758%   $86.9715   $86.97   $86.95   $87.00  
  Purchase #5 $77.39   5.539%   $81.6766   $81.68   $81.70   $81.70  
  Purchase #6 $187.99   4.304%   $196.0811   $196.08   $196.10   $196.10  
  Purchase #7 $43.69   11.291%   $48.623   $48.62   $48.60   $48.60  
  7 purchase totals = $866.26       $914.4966   $914.49   $914.45   $914.60