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	$93.59	7.555%	$100.6607	$100.66	$100.65	$100.70
Purchase #2	$100.31	10.729%	$111.0723	$111.07	$111.05	$111.10
Purchase #3	$149.72	8.819%	$162.9238	$162.92	$162.90	$162.90
Purchase #4	$221.56	5.634%	$234.0427	$234.04	$234.05	$234.00
Purchase #5	$157.40	10.805%	$174.4071	$174.41	$174.40	$174.40
Purchase #6	$99.32	13.143%	$112.3736	$112.37	$112.35	$112.40
Purchase #7	$22.46	3.220%	$23.1832	$23.18	$23.20	$23.20
7 purchase totals =	$844.36		$918.6634	$918.65	$918.60	$918.70