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	$29.26	9.718%	$32.1035	$32.10	$32.10	$32.10
Purchase #2	$132.48	13.107%	$149.8442	$149.84	$149.85	$149.80
Purchase #3	$88.78	10.779%	$98.3496	$98.35	$98.35	$98.30
Purchase #4	$127.78	12.578%	$143.8522	$143.85	$143.85	$143.90
Purchase #5	$166.36	7.865%	$179.4442	$179.44	$179.45	$179.40
Purchase #6	$54.53	9.464%	$59.6907	$59.69	$59.70	$59.70
Purchase #7	$41.56	4.648%	$43.4917	$43.49	$43.50	$43.50
7 purchase totals =	$640.75		$706.7761	$706.76	$706.80	$706.70