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	$48.78	13.403%	$55.318	$55.32	$55.30	$55.30
Purchase #2	$123.43	13.129%	$139.6351	$139.64	$139.65	$139.60
Purchase #3	$90.99	9.166%	$99.3301	$99.33	$99.35	$99.30
Purchase #4	$204.55	10.292%	$225.6023	$225.60	$225.60	$225.60
Purchase #5	$250.89	12.278%	$281.6943	$281.69	$281.70	$281.70
Purchase #6	$245.95	9.229%	$268.6487	$268.65	$268.65	$268.60
Purchase #7	$72.33	10.172%	$79.6874	$79.69	$79.70	$79.70
7 purchase totals =	$1,036.92		$1,149.9159	$1,149.92	$1,149.95	$1,149.80