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	$168.99	12.849%	$190.7035	$190.70	$190.70	$190.70
Purchase #2	$82.82	13.834%	$94.2773	$94.28	$94.30	$94.30
Purchase #3	$35.75	7.511%	$38.4352	$38.44	$38.45	$38.40
Purchase #4	$37.46	7.520%	$40.277	$40.28	$40.30	$40.30
Purchase #5	$125.25	13.603%	$142.2878	$142.29	$142.30	$142.30
Purchase #6	$82.49	3.259%	$85.1783	$85.18	$85.20	$85.20
Purchase #7	$52.56	7.852%	$56.687	$56.69	$56.70	$56.70
7 purchase totals =	$585.32		$647.8461	$647.86	$647.95	$647.90