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	$79.52	13.338%	$90.1264	$90.13	$90.15	$90.10
Purchase #2	$64.43	8.612%	$69.9787	$69.98	$70.00	$70.00
Purchase #3	$7.50	4.519%	$7.8389	$7.84	$7.85	$7.80
Purchase #4	$133.71	12.111%	$149.9036	$149.90	$149.90	$149.90
Purchase #5	$49.98	13.254%	$56.6043	$56.60	$56.60	$56.60
Purchase #6	$110.50	6.199%	$117.3499	$117.35	$117.35	$117.30
Purchase #7	$38.89	11.235%	$43.2593	$43.26	$43.25	$43.30
7 purchase totals =	$484.53		$535.0611	$535.06	$535.10	$535.00