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	$31.54	6.234%	$33.5062	$33.51	$33.50	$33.50
Purchase #2	$155.75	4.319%	$162.4768	$162.48	$162.50	$162.50
Purchase #3	$61.92	9.308%	$67.6835	$67.68	$67.70	$67.70
Purchase #4	$128.94	9.591%	$141.3066	$141.31	$141.30	$141.30
Purchase #5	$121.26	9.324%	$132.5663	$132.57	$132.55	$132.60
Purchase #6	$30.85	11.144%	$34.2879	$34.29	$34.30	$34.30
Purchase #7	$28.37	10.831%	$31.4428	$31.44	$31.45	$31.40
7 purchase totals =	$558.63		$603.2701	$603.28	$603.30	$603.30