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	$96.94	8.199%	$104.8881	$104.89	$104.90	$104.90
Purchase #2	$46.56	10.371%	$51.3887	$51.39	$51.40	$51.40
Purchase #3	$28.83	4.117%	$30.0169	$30.02	$30.00	$30.00
Purchase #4	$32.51	3.456%	$33.6335	$33.63	$33.65	$33.60
Purchase #5	$60.59	12.102%	$67.9226	$67.92	$67.90	$67.90
Purchase #6	$33.83	5.602%	$35.7252	$35.73	$35.75	$35.70
Purchase #7	$180.33	4.792%	$188.9714	$188.97	$188.95	$189.00
7 purchase totals =	$479.59		$512.5464	$512.55	$512.55	$512.50