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	$83.91	6.688%	$89.5219	$89.52	$89.50	$89.50
Purchase #2	$81.43	12.799%	$91.8522	$91.85	$91.85	$91.90
Purchase #3	$36.60	11.348%	$40.7534	$40.75	$40.75	$40.80
Purchase #4	$150.51	11.354%	$167.5989	$167.60	$167.60	$167.60
Purchase #5	$91.96	7.688%	$99.0299	$99.03	$99.05	$99.00
Purchase #6	$147.34	3.446%	$152.4173	$152.42	$152.40	$152.40
Purchase #7	$231.82	8.179%	$250.7806	$250.78	$250.80	$250.80
7 purchase totals =	$823.57		$891.9542	$891.95	$891.95	$892.00