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	$212.73	12.284%	$238.8618	$238.86	$238.85	$238.90
Purchase #2	$39.69	7.249%	$42.5671	$42.57	$42.55	$42.60
Purchase #3	$78.40	5.516%	$82.7245	$82.72	$82.70	$82.70
Purchase #4	$56.85	9.263%	$62.116	$62.12	$62.10	$62.10
Purchase #5	$223.71	9.791%	$245.6134	$245.61	$245.60	$245.60
Purchase #6	$152.34	13.250%	$172.5251	$172.53	$172.55	$172.50
Purchase #7	$19.58	12.370%	$22.002	$22.00	$22.00	$22.00
7 purchase totals =	$783.30		$866.4099	$866.41	$866.35	$866.40