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	$82.83	11.447%	$92.3116	$92.31	$92.30	$92.30
Purchase #2	$105.57	3.363%	$109.1203	$109.12	$109.10	$109.10
Purchase #3	$90.40	9.475%	$98.9654	$98.97	$98.95	$99.00
Purchase #4	$90.38	12.323%	$101.5175	$101.52	$101.50	$101.50
Purchase #5	$10.50	4.288%	$10.9502	$10.95	$10.95	$11.00
Purchase #6	$93.73	5.571%	$98.9517	$98.95	$98.95	$99.00
Purchase #7	$171.79	4.227%	$179.0516	$179.05	$179.05	$179.10
7 purchase totals =	$645.20		$690.8683	$690.87	$690.80	$691.00