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	$74.78	12.204%	$83.9062	$83.91	$83.90	$83.90
Purchase #2	$12.65	11.843%	$14.1481	$14.15	$14.15	$14.10
Purchase #3	$107.49	5.728%	$113.647	$113.65	$113.65	$113.60
Purchase #4	$127.84	11.722%	$142.8254	$142.83	$142.85	$142.80
Purchase #5	$249.52	5.822%	$264.0471	$264.05	$264.05	$264.00
Purchase #6	$169.39	3.541%	$175.3881	$175.39	$175.40	$175.40
Purchase #7	$148.64	9.158%	$162.2525	$162.25	$162.25	$162.30
7 purchase totals =	$890.31		$956.2144	$956.23	$956.25	$956.10