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	$221.63	12.670%	$249.7105	$249.71	$249.70	$249.70
Purchase #2	$114.56	7.461%	$123.1073	$123.11	$123.10	$123.10
Purchase #3	$17.74	11.608%	$19.7993	$19.80	$19.80	$19.80
Purchase #4	$234.31	8.789%	$254.9035	$254.90	$254.90	$254.90
Purchase #5	$39.58	5.695%	$41.8341	$41.83	$41.85	$41.80
Purchase #6	$98.41	5.521%	$103.8432	$103.84	$103.85	$103.80
Purchase #7	$51.78	3.578%	$53.6327	$53.63	$53.65	$53.60
7 purchase totals =	$778.01		$846.8306	$846.82	$846.85	$846.70