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	$211.77	12.619%	$238.4933	$238.49	$238.50	$238.50
Purchase #2	$139.77	9.539%	$153.1027	$153.10	$153.10	$153.10
Purchase #3	$112.82	13.199%	$127.7111	$127.71	$127.70	$127.70
Purchase #4	$228.56	4.284%	$238.3515	$238.35	$238.35	$238.40
Purchase #5	$229.99	7.319%	$246.823	$246.82	$246.80	$246.80
Purchase #6	$47.90	3.417%	$49.5367	$49.54	$49.55	$49.50
Purchase #7	$33.89	7.720%	$36.5063	$36.51	$36.50	$36.50
7 purchase totals =	$1,004.70		$1,090.5246	$1,090.52	$1,090.50	$1,090.50