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	$236.71	8.289%	$256.3309	$256.33	$256.35	$256.30
Purchase #2	$218.47	9.604%	$239.4519	$239.45	$239.45	$239.50
Purchase #3	$95.93	3.429%	$99.2194	$99.22	$99.20	$99.20
Purchase #4	$154.42	11.503%	$172.1829	$172.18	$172.20	$172.20
Purchase #5	$47.78	4.464%	$49.9129	$49.91	$49.90	$49.90
Purchase #6	$159.57	12.234%	$179.0918	$179.09	$179.10	$179.10
Purchase #7	$216.43	3.190%	$223.3341	$223.33	$223.35	$223.30
7 purchase totals =	$1,129.31		$1,219.5239	$1,219.51	$1,219.55	$1,219.50