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	$5.75	10.744%	$6.3678	$6.37	$6.35	$6.40
Purchase #2	$72.35	13.319%	$81.9863	$81.99	$82.00	$82.00
Purchase #3	$124.60	13.740%	$141.72	$141.72	$141.70	$141.70
Purchase #4	$159.39	13.613%	$181.0878	$181.09	$181.10	$181.10
Purchase #5	$64.41	11.182%	$71.6123	$71.61	$71.60	$71.60
Purchase #6	$40.90	3.267%	$42.2362	$42.24	$42.25	$42.20
Purchase #7	$121.83	5.238%	$128.2115	$128.21	$128.20	$128.20
7 purchase totals =	$589.23		$653.2219	$653.23	$653.20	$653.20