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	$134.61	13.112%	$152.2601	$152.26	$152.25	$152.30
Purchase #2	$123.49	13.510%	$140.1735	$140.17	$140.15	$140.20
Purchase #3	$56.42	8.450%	$61.1875	$61.19	$61.20	$61.20
Purchase #4	$130.59	12.154%	$146.4619	$146.46	$146.45	$146.50
Purchase #5	$198.96	3.355%	$205.6351	$205.64	$205.65	$205.60
Purchase #6	$133.34	13.341%	$151.1289	$151.13	$151.15	$151.10
Purchase #7	$80.87	10.387%	$89.27	$89.27	$89.25	$89.30
7 purchase totals =	$858.28		$946.1170	$946.12	$946.10	$946.20