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	$208.76	9.290%	$228.1538	$228.15	$228.15	$228.20
Purchase #2	$37.75	12.769%	$42.5703	$42.57	$42.55	$42.60
Purchase #3	$57.58	11.111%	$63.9777	$63.98	$64.00	$64.00
Purchase #4	$96.49	7.120%	$103.3601	$103.36	$103.35	$103.40
Purchase #5	$230.55	12.796%	$260.0512	$260.05	$260.05	$260.10
Purchase #6	$74.75	4.398%	$78.0375	$78.04	$78.05	$78.00
Purchase #7	$70.51	11.601%	$78.6899	$78.69	$78.70	$78.70
7 purchase totals =	$776.39		$854.8405	$854.84	$854.85	$855.00