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	$55.36	5.260%	$58.2719	$58.27	$58.25	$58.30
Purchase #2	$85.43	4.342%	$89.1394	$89.14	$89.15	$89.10
Purchase #3	$250.66	12.266%	$281.406	$281.41	$281.40	$281.40
Purchase #4	$165.77	5.343%	$174.6271	$174.63	$174.65	$174.60
Purchase #5	$96.31	8.535%	$104.5301	$104.53	$104.55	$104.50
Purchase #6	$56.41	11.677%	$62.997	$63.00	$63.00	$63.00
Purchase #7	$185.95	13.177%	$210.4526	$210.45	$210.45	$210.50
7 purchase totals =	$895.89		$981.4241	$981.43	$981.45	$981.40