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	$126.33	10.764%	$139.9282	$139.93	$139.95	$139.90
Purchase #2	$79.50	12.113%	$89.1298	$89.13	$89.15	$89.10
Purchase #3	$150.65	11.776%	$168.3905	$168.39	$168.40	$168.40
Purchase #4	$40.87	10.752%	$45.2643	$45.26	$45.25	$45.30
Purchase #5	$173.89	7.399%	$186.7561	$186.76	$186.75	$186.80
Purchase #6	$235.60	4.817%	$246.9489	$246.95	$246.95	$246.90
Purchase #7	$12.36	6.223%	$13.1292	$13.13	$13.15	$13.10
7 purchase totals =	$819.20		$889.5470	$889.55	$889.60	$889.50