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	$221.86	5.150%	$233.2858	$233.29	$233.30	$233.30
Purchase #2	$171.91	6.309%	$182.7558	$182.76	$182.75	$182.80
Purchase #3	$153.56	12.492%	$172.7427	$172.74	$172.75	$172.70
Purchase #4	$87.30	10.689%	$96.6315	$96.63	$96.65	$96.60
Purchase #5	$33.32	6.553%	$35.5035	$35.50	$35.50	$35.50
Purchase #6	$134.82	3.179%	$139.1059	$139.11	$139.10	$139.10
Purchase #7	$90.41	3.298%	$93.3917	$93.39	$93.40	$93.40
7 purchase totals =	$893.18		$953.4169	$953.42	$953.45	$953.40