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	$40.74	3.214%	$42.0494	$42.05	$42.05	$42.00
Purchase #2	$70.32	6.476%	$74.8739	$74.87	$74.85	$74.90
Purchase #3	$183.61	9.691%	$201.4036	$201.40	$201.40	$201.40
Purchase #4	$245.79	12.352%	$276.15	$276.15	$276.15	$276.20
Purchase #5	$122.60	4.823%	$128.513	$128.51	$128.50	$128.50
Purchase #6	$67.76	4.814%	$71.022	$71.02	$71.00	$71.00
Purchase #7	$249.30	7.225%	$267.3119	$267.31	$267.30	$267.30
7 purchase totals =	$980.12		$1,061.3238	$1,061.31	$1,061.25	$1,061.30