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	$37.43	12.272%	$42.0234	$42.02	$42.00	$42.00
Purchase #2	$145.78	3.511%	$150.8983	$150.90	$150.90	$150.90
Purchase #3	$172.83	11.629%	$192.9284	$192.93	$192.95	$192.90
Purchase #4	$37.69	3.796%	$39.1207	$39.12	$39.10	$39.10
Purchase #5	$20.38	4.386%	$21.2739	$21.27	$21.25	$21.30
Purchase #6	$94.41	3.454%	$97.6709	$97.67	$97.65	$97.70
Purchase #7	$233.38	6.149%	$247.7305	$247.73	$247.75	$247.70
7 purchase totals =	$741.90		$791.6461	$791.64	$791.60	$791.60