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	$38.42	12.596%	$43.2594	$43.26	$43.25	$43.30
Purchase #2	$6.81	3.721%	$7.0634	$7.06	$7.05	$7.10
Purchase #3	$39.43	6.760%	$42.0955	$42.10	$42.10	$42.10
Purchase #4	$211.29	10.711%	$233.9213	$233.92	$233.90	$233.90
Purchase #5	$5.54	9.286%	$6.0544	$6.05	$6.05	$6.10
Purchase #6	$33.54	7.782%	$36.1501	$36.15	$36.15	$36.20
Purchase #7	$170.51	11.365%	$189.8885	$189.89	$189.90	$189.90
7 purchase totals =	$505.54		$558.4326	$558.43	$558.40	$558.60