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	$179.44	4.152%	$186.8903	$186.89	$186.90	$186.90
Purchase #2	$145.78	11.845%	$163.0476	$163.05	$163.05	$163.00
Purchase #3	$42.69	7.631%	$45.9477	$45.95	$45.95	$45.90
Purchase #4	$242.46	3.231%	$250.2939	$250.29	$250.30	$250.30
Purchase #5	$53.32	3.268%	$55.0625	$55.06	$55.05	$55.10
Purchase #6	$186.85	6.253%	$198.5337	$198.53	$198.55	$198.50
Purchase #7	$248.78	12.339%	$279.477	$279.48	$279.50	$279.50
7 purchase totals =	$1,099.32		$1,179.2527	$1,179.25	$1,179.30	$1,179.20