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	$204.78	8.175%	$221.5208	$221.52	$221.50	$221.50
Purchase #2	$133.31	13.179%	$150.8789	$150.88	$150.90	$150.90
Purchase #3	$67.96	12.418%	$76.3993	$76.40	$76.40	$76.40
Purchase #4	$152.82	11.333%	$170.1391	$170.14	$170.15	$170.10
Purchase #5	$94.82	4.589%	$99.1713	$99.17	$99.15	$99.20
Purchase #6	$27.37	8.206%	$29.616	$29.62	$29.60	$29.60
Purchase #7	$229.69	10.236%	$253.2011	$253.20	$253.20	$253.20
7 purchase totals =	$910.75		$1,000.9265	$1,000.93	$1,000.90	$1,000.90