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	$158.88	3.228%	$164.0086	$164.01	$164.00	$164.00
Purchase #2	$248.95	6.202%	$264.3899	$264.39	$264.40	$264.40
Purchase #3	$84.72	7.805%	$91.3324	$91.33	$91.35	$91.30
Purchase #4	$22.95	10.258%	$25.3042	$25.30	$25.30	$25.30
Purchase #5	$155.64	10.140%	$171.4219	$171.42	$171.40	$171.40
Purchase #6	$56.26	8.750%	$61.1828	$61.18	$61.20	$61.20
Purchase #7	$38.49	10.153%	$42.3979	$42.40	$42.40	$42.40
7 purchase totals =	$765.89		$820.0377	$820.03	$820.05	$820.00