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	$170.54	5.744%	$180.3358	$180.34	$180.35	$180.30
Purchase #2	$113.52	3.582%	$117.5863	$117.59	$117.60	$117.60
Purchase #3	$84.51	7.200%	$90.5947	$90.59	$90.60	$90.60
Purchase #4	$148.54	7.468%	$159.633	$159.63	$159.65	$159.60
Purchase #5	$150.43	5.119%	$158.1305	$158.13	$158.15	$158.10
Purchase #6	$129.64	3.166%	$133.7444	$133.74	$133.75	$133.70
Purchase #7	$89.56	11.744%	$100.0779	$100.08	$100.10	$100.10
7 purchase totals =	$886.74		$940.1026	$940.10	$940.20	$940.00