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	$50.88	9.150%	$55.5355	$55.54	$55.55	$55.50
Purchase #2	$103.33	9.443%	$113.0875	$113.09	$113.10	$113.10
Purchase #3	$130.61	10.430%	$144.2326	$144.23	$144.25	$144.20
Purchase #4	$109.84	3.124%	$113.2714	$113.27	$113.25	$113.30
Purchase #5	$233.52	3.638%	$242.0155	$242.02	$242.00	$242.00
Purchase #6	$172.31	13.623%	$195.7838	$195.78	$195.80	$195.80
Purchase #7	$54.89	3.341%	$56.7239	$56.72	$56.70	$56.70
7 purchase totals =	$855.38		$920.6502	$920.65	$920.65	$920.60