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	$214.45	4.124%	$223.2939	$223.29	$223.30	$223.30
Purchase #2	$133.30	4.747%	$139.6278	$139.63	$139.65	$139.60
Purchase #3	$72.33	11.854%	$80.904	$80.90	$80.90	$80.90
Purchase #4	$29.61	10.300%	$32.6598	$32.66	$32.65	$32.70
Purchase #5	$222.88	11.337%	$248.1479	$248.15	$248.15	$248.10
Purchase #6	$31.75	11.832%	$35.5067	$35.51	$35.50	$35.50
Purchase #7	$116.27	12.280%	$130.548	$130.55	$130.55	$130.50
7 purchase totals =	$820.59		$890.6881	$890.69	$890.70	$890.60