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	$84.68	7.348%	$90.9023	$90.90	$90.90	$90.90
Purchase #2	$30.94	3.580%	$32.0477	$32.05	$32.05	$32.00
Purchase #3	$29.91	11.625%	$33.387	$33.39	$33.40	$33.40
Purchase #4	$99.47	12.764%	$112.1664	$112.17	$112.15	$112.20
Purchase #5	$54.76	4.515%	$57.2324	$57.23	$57.25	$57.20
Purchase #6	$250.75	11.303%	$279.0923	$279.09	$279.10	$279.10
Purchase #7	$158.66	11.284%	$176.5632	$176.56	$176.55	$176.60
7 purchase totals =	$709.17		$781.3913	$781.39	$781.40	$781.40