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	$249.33	10.424%	$275.3202	$275.32	$275.30	$275.30
Purchase #2	$5.69	13.470%	$6.4564	$6.46	$6.45	$6.50
Purchase #3	$75.72	8.771%	$82.3614	$82.36	$82.35	$82.40
Purchase #4	$121.40	9.125%	$132.4778	$132.48	$132.50	$132.50
Purchase #5	$32.72	6.781%	$34.9387	$34.94	$34.95	$34.90
Purchase #6	$28.28	4.465%	$29.5427	$29.54	$29.55	$29.50
Purchase #7	$76.81	11.761%	$85.8436	$85.84	$85.85	$85.80
7 purchase totals =	$589.95		$646.9408	$646.94	$646.95	$646.90