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	$243.71	12.801%	$274.9073	$274.91	$274.90	$274.90
Purchase #2	$101.77	7.123%	$109.0191	$109.02	$109.00	$109.00
Purchase #3	$189.28	5.693%	$200.0557	$200.06	$200.05	$200.10
Purchase #4	$126.67	13.287%	$143.5006	$143.50	$143.50	$143.50
Purchase #5	$6.65	13.432%	$7.5432	$7.54	$7.55	$7.50
Purchase #6	$165.30	13.547%	$187.6932	$187.69	$187.70	$187.70
Purchase #7	$175.53	4.749%	$183.8659	$183.87	$183.85	$183.90
7 purchase totals =	$1,008.91		$1,106.5850	$1,106.59	$1,106.55	$1,106.60