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	$248.48	7.750%	$267.7372	$267.74	$267.75	$267.70
Purchase #2	$95.47	3.422%	$98.737	$98.74	$98.75	$98.70
Purchase #3	$103.60	13.245%	$117.3218	$117.32	$117.30	$117.30
Purchase #4	$54.38	4.384%	$56.764	$56.76	$56.75	$56.80
Purchase #5	$45.32	11.418%	$50.4946	$50.49	$50.50	$50.50
Purchase #6	$52.29	4.188%	$54.4799	$54.48	$54.50	$54.50
Purchase #7	$42.75	7.281%	$45.8626	$45.86	$45.85	$45.90
7 purchase totals =	$642.29		$691.3971	$691.39	$691.40	$691.40