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	$170.34	4.336%	$177.7259	$177.73	$177.75	$177.70
Purchase #2	$28.52	9.833%	$31.3244	$31.32	$31.30	$31.30
Purchase #3	$232.73	3.484%	$240.8383	$240.84	$240.85	$240.80
Purchase #4	$55.59	12.687%	$62.6427	$62.64	$62.65	$62.60
Purchase #5	$170.72	11.515%	$190.3784	$190.38	$190.40	$190.40
Purchase #6	$97.73	5.739%	$103.3387	$103.34	$103.35	$103.30
Purchase #7	$162.98	3.400%	$168.5213	$168.52	$168.50	$168.50
7 purchase totals =	$918.61		$974.7697	$974.77	$974.80	$974.60