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	$171.32	10.160%	$188.7261	$188.73	$188.75	$188.70
Purchase #2	$241.36	3.772%	$250.4641	$250.46	$250.45	$250.50
Purchase #3	$202.33	10.594%	$223.7648	$223.76	$223.75	$223.80
Purchase #4	$220.26	12.481%	$247.7507	$247.75	$247.75	$247.80
Purchase #5	$146.71	10.326%	$161.8593	$161.86	$161.85	$161.90
Purchase #6	$148.82	10.642%	$164.6574	$164.66	$164.65	$164.70
Purchase #7	$68.37	4.536%	$71.4713	$71.47	$71.45	$71.50
7 purchase totals =	$1,199.17		$1,308.6937	$1,308.69	$1,308.65	$1,308.90