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	$22.30	4.112%	$23.217	$23.22	$23.20	$23.20
Purchase #2	$52.83	11.346%	$58.8241	$58.82	$58.80	$58.80
Purchase #3	$53.47	11.670%	$59.7099	$59.71	$59.70	$59.70
Purchase #4	$70.31	11.214%	$78.1946	$78.19	$78.20	$78.20
Purchase #5	$85.65	6.560%	$91.2686	$91.27	$91.25	$91.30
Purchase #6	$97.69	8.386%	$105.8823	$105.88	$105.90	$105.90
Purchase #7	$219.71	9.698%	$241.0175	$241.02	$241.00	$241.00
7 purchase totals =	$601.96		$658.1140	$658.11	$658.05	$658.10