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	$120.52	5.546%	$127.204	$127.20	$127.20	$127.20
Purchase #2	$159.43	5.820%	$168.7088	$168.71	$168.70	$168.70
Purchase #3	$82.63	4.793%	$86.5905	$86.59	$86.60	$86.60
Purchase #4	$17.39	11.682%	$19.4215	$19.42	$19.40	$19.40
Purchase #5	$6.57	11.773%	$7.3435	$7.34	$7.35	$7.30
Purchase #6	$96.66	12.571%	$108.8111	$108.81	$108.80	$108.80
Purchase #7	$33.51	6.120%	$35.5608	$35.56	$35.55	$35.60
7 purchase totals =	$516.71		$553.6402	$553.63	$553.60	$553.60