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	$19.50	4.627%	$20.4023	$20.40	$20.40	$20.40
Purchase #2	$68.34	6.650%	$72.8846	$72.88	$72.90	$72.90
Purchase #3	$61.71	10.864%	$68.4142	$68.41	$68.40	$68.40
Purchase #4	$85.44	6.683%	$91.15	$91.15	$91.15	$91.20
Purchase #5	$20.63	9.862%	$22.6645	$22.66	$22.65	$22.70
Purchase #6	$45.29	4.740%	$47.4367	$47.44	$47.45	$47.40
Purchase #7	$153.32	8.151%	$165.8171	$165.82	$165.80	$165.80
7 purchase totals =	$454.23		$488.7694	$488.76	$488.75	$488.80