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	$96.69	3.214%	$99.7976	$99.80	$99.80	$99.80
Purchase #2	$29.63	9.214%	$32.3601	$32.36	$32.35	$32.40
Purchase #3	$167.87	13.612%	$190.7205	$190.72	$190.70	$190.70
Purchase #4	$174.35	5.679%	$184.2513	$184.25	$184.25	$184.30
Purchase #5	$233.89	13.662%	$265.8441	$265.84	$265.85	$265.80
Purchase #6	$120.75	8.850%	$131.4364	$131.44	$131.45	$131.40
Purchase #7	$172.98	4.584%	$180.9094	$180.91	$180.90	$180.90
7 purchase totals =	$996.16		$1,085.3194	$1,085.32	$1,085.30	$1,085.30