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	$129.55	11.684%	$144.6866	$144.69	$144.70	$144.70
Purchase #2	$52.37	10.602%	$57.9223	$57.92	$57.90	$57.90
Purchase #3	$115.87	13.443%	$131.4464	$131.45	$131.45	$131.40
Purchase #4	$128.56	7.263%	$137.8973	$137.90	$137.90	$137.90
Purchase #5	$93.61	3.752%	$97.1222	$97.12	$97.10	$97.10
Purchase #6	$141.61	3.621%	$146.7377	$146.74	$146.75	$146.70
Purchase #7	$107.32	5.206%	$112.9071	$112.91	$112.90	$112.90
7 purchase totals =	$768.89		$828.7196	$828.73	$828.70	$828.60