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	$216.84	3.245%	$223.8765	$223.88	$223.90	$223.90
Purchase #2	$36.40	11.200%	$40.4768	$40.48	$40.50	$40.50
Purchase #3	$26.83	12.219%	$30.1084	$30.11	$30.10	$30.10
Purchase #4	$180.33	10.823%	$199.8471	$199.85	$199.85	$199.80
Purchase #5	$168.32	10.105%	$185.3287	$185.33	$185.35	$185.30
Purchase #6	$204.49	9.168%	$223.2376	$223.24	$223.25	$223.20
Purchase #7	$96.31	9.689%	$105.6415	$105.64	$105.65	$105.60
7 purchase totals =	$929.52		$1,008.5166	$1,008.53	$1,008.60	$1,008.40