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 $85.95   12.748%   $96.9069   $96.91   $96.90   $96.90  
  Purchase #2 $156.91   12.604%   $176.6869   $176.69   $176.70   $176.70  
  Purchase #3 $235.28   3.813%   $244.2512   $244.25   $244.25   $244.30  
  Purchase #4 $131.27   10.170%   $144.6202   $144.62   $144.60   $144.60  
  Purchase #5 $19.71   11.314%   $21.94   $21.94   $21.95   $21.90  
  Purchase #6 $36.91   13.403%   $41.857   $41.86   $41.85   $41.90  
  Purchase #7 $208.47   4.628%   $218.118   $218.12   $218.10   $218.10  
  7 purchase totals = $874.50       $944.3802   $944.39   $944.35   $944.40