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	$146.31	6.361%	$155.6168	$155.62	$155.60	$155.60
Purchase #2	$136.83	4.401%	$142.8519	$142.85	$142.85	$142.90
Purchase #3	$43.57	10.670%	$48.2189	$48.22	$48.20	$48.20
Purchase #4	$225.46	11.692%	$251.8208	$251.82	$251.80	$251.80
Purchase #5	$43.50	4.855%	$45.6119	$45.61	$45.60	$45.60
Purchase #6	$62.85	10.778%	$69.624	$69.62	$69.60	$69.60
Purchase #7	$99.50	6.776%	$106.2421	$106.24	$106.25	$106.20
7 purchase totals =	$758.02		$819.9864	$819.98	$819.90	$819.90