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 $67.48   9.278%   $73.7408   $73.74   $73.75   $73.70  
  Purchase #2 $40.84   9.821%   $44.8509   $44.85   $44.85   $44.90  
  Purchase #3 $187.72   10.539%   $207.5038   $207.50   $207.50   $207.50  
  Purchase #4 $38.73   10.477%   $42.7877   $42.79   $42.80   $42.80  
  Purchase #5 $186.98   3.722%   $193.9394   $193.94   $193.95   $193.90  
  Purchase #6 $165.42   10.469%   $182.7378   $182.74   $182.75   $182.70  
  Purchase #7 $168.28   13.197%   $190.4879   $190.49   $190.50   $190.50  
  7 purchase totals = $855.45       $936.0483   $936.05   $936.10   $936.00