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	$25.61	11.711%	$28.6092	$28.61	$28.60	$28.60
Purchase #2	$148.31	4.695%	$155.2732	$155.27	$155.25	$155.30
Purchase #3	$52.92	9.237%	$57.8082	$57.81	$57.80	$57.80
Purchase #4	$183.43	3.522%	$189.8904	$189.89	$189.90	$189.90
Purchase #5	$141.82	10.549%	$156.7806	$156.78	$156.80	$156.80
Purchase #6	$26.56	6.727%	$28.3467	$28.35	$28.35	$28.30
Purchase #7	$47.69	13.278%	$54.0223	$54.02	$54.00	$54.00
7 purchase totals =	$626.34		$670.7306	$670.73	$670.70	$670.70