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	$119.92	10.454%	$132.4564	$132.46	$132.45	$132.50
Purchase #2	$133.47	6.371%	$141.9734	$141.97	$141.95	$142.00
Purchase #3	$229.73	7.598%	$247.1849	$247.18	$247.20	$247.20
Purchase #4	$111.41	3.508%	$115.3183	$115.32	$115.30	$115.30
Purchase #5	$132.76	9.771%	$145.732	$145.73	$145.75	$145.70
Purchase #6	$39.46	7.112%	$42.2664	$42.27	$42.25	$42.30
Purchase #7	$90.59	5.532%	$95.6014	$95.60	$95.60	$95.60
7 purchase totals =	$857.34		$920.5328	$920.53	$920.50	$920.60