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	$248.57	13.129%	$281.2048	$281.20	$281.20	$281.20
Purchase #2	$208.90	13.406%	$236.9051	$236.91	$236.90	$236.90
Purchase #3	$118.26	4.802%	$123.9388	$123.94	$123.95	$123.90
Purchase #4	$222.99	8.767%	$242.5395	$242.54	$242.55	$242.50
Purchase #5	$152.33	7.291%	$163.4364	$163.44	$163.45	$163.40
Purchase #6	$79.62	12.135%	$89.2819	$89.28	$89.30	$89.30
Purchase #7	$53.38	11.597%	$59.5705	$59.57	$59.55	$59.60
7 purchase totals =	$1,084.05		$1,196.8770	$1,196.88	$1,196.90	$1,196.80