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	$233.69	11.632%	$260.8728	$260.87	$260.85	$260.90
Purchase #2	$186.38	10.751%	$206.4177	$206.42	$206.40	$206.40
Purchase #3	$58.78	6.308%	$62.4878	$62.49	$62.50	$62.50
Purchase #4	$35.39	7.342%	$37.9883	$37.99	$38.00	$38.00
Purchase #5	$119.36	10.283%	$131.6338	$131.63	$131.65	$131.60
Purchase #6	$99.44	4.490%	$103.9049	$103.90	$103.90	$103.90
Purchase #7	$16.27	6.494%	$17.3266	$17.33	$17.35	$17.30
7 purchase totals =	$749.31		$820.6319	$820.63	$820.65	$820.60