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	$20.38	3.168%	$21.0256	$21.03	$21.05	$21.00
Purchase #2	$64.67	4.351%	$67.4838	$67.48	$67.50	$67.50
Purchase #3	$133.33	13.276%	$151.0309	$151.03	$151.05	$151.00
Purchase #4	$230.59	13.351%	$261.3761	$261.38	$261.40	$261.40
Purchase #5	$173.65	3.178%	$179.1686	$179.17	$179.15	$179.20
Purchase #6	$149.32	3.159%	$154.037	$154.04	$154.05	$154.00
Purchase #7	$170.37	5.751%	$180.168	$180.17	$180.15	$180.20
7 purchase totals =	$942.31		$1,014.2900	$1,014.30	$1,014.35	$1,014.30