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	$22.58	12.109%	$25.3142	$25.31	$25.30	$25.30
Purchase #2	$106.98	6.177%	$113.5882	$113.59	$113.60	$113.60
Purchase #3	$29.82	6.764%	$31.837	$31.84	$31.85	$31.80
Purchase #4	$18.45	13.504%	$20.9415	$20.94	$20.95	$20.90
Purchase #5	$60.41	3.261%	$62.38	$62.38	$62.40	$62.40
Purchase #6	$31.56	8.728%	$34.3146	$34.31	$34.30	$34.30
Purchase #7	$188.90	11.361%	$210.3609	$210.36	$210.35	$210.40
7 purchase totals =	$458.70		$498.7364	$498.73	$498.75	$498.70