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	$119.29	12.500%	$134.2013	$134.20	$134.20	$134.20
Purchase #2	$44.73	13.129%	$50.6026	$50.60	$50.60	$50.60
Purchase #3	$175.95	11.698%	$196.5326	$196.53	$196.55	$196.50
Purchase #4	$115.87	3.484%	$119.9069	$119.91	$119.90	$119.90
Purchase #5	$152.45	12.354%	$171.2837	$171.28	$171.30	$171.30
Purchase #6	$114.28	11.300%	$127.1936	$127.19	$127.20	$127.20
Purchase #7	$37.62	9.790%	$41.303	$41.30	$41.30	$41.30
7 purchase totals =	$760.19		$841.0237	$841.01	$841.05	$841.00