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	$134.36	4.219%	$140.0286	$140.03	$140.05	$140.00
Purchase #2	$86.66	4.268%	$90.3586	$90.36	$90.35	$90.40
Purchase #3	$146.48	10.826%	$162.3379	$162.34	$162.35	$162.30
Purchase #4	$19.56	4.363%	$20.4134	$20.41	$20.40	$20.40
Purchase #5	$64.72	4.612%	$67.7049	$67.70	$67.70	$67.70
Purchase #6	$24.26	4.411%	$25.3301	$25.33	$25.35	$25.30
Purchase #7	$169.28	7.222%	$181.5054	$181.51	$181.50	$181.50
7 purchase totals =	$645.32		$687.6789	$687.68	$687.70	$687.60