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	$49.95	10.670%	$55.2797	$55.28	$55.30	$55.30
Purchase #2	$184.56	6.426%	$196.4198	$196.42	$196.40	$196.40
Purchase #3	$40.48	11.867%	$45.2838	$45.28	$45.30	$45.30
Purchase #4	$94.80	4.164%	$98.7475	$98.75	$98.75	$98.70
Purchase #5	$115.91	13.739%	$131.8349	$131.83	$131.85	$131.80
Purchase #6	$93.79	11.378%	$104.4614	$104.46	$104.45	$104.50
Purchase #7	$167.29	13.393%	$189.6951	$189.70	$189.70	$189.70
7 purchase totals =	$746.78		$821.7222	$821.72	$821.75	$821.70