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	$90.93	3.677%	$94.2735	$94.27	$94.25	$94.30
Purchase #2	$158.69	8.692%	$172.4833	$172.48	$172.50	$172.50
Purchase #3	$55.82	7.326%	$59.9094	$59.91	$59.90	$59.90
Purchase #4	$139.83	12.346%	$157.0934	$157.09	$157.10	$157.10
Purchase #5	$27.63	12.421%	$31.0619	$31.06	$31.05	$31.10
Purchase #6	$230.30	5.210%	$242.2986	$242.30	$242.30	$242.30
Purchase #7	$25.39	7.613%	$27.3229	$27.32	$27.30	$27.30
7 purchase totals =	$728.59		$784.4430	$784.43	$784.40	$784.50