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	$158.90	12.120%	$178.1587	$178.16	$178.15	$178.20
Purchase #2	$225.35	4.164%	$234.7336	$234.73	$234.75	$234.70
Purchase #3	$84.51	9.263%	$92.3382	$92.34	$92.35	$92.30
Purchase #4	$208.45	6.559%	$222.1222	$222.12	$222.10	$222.10
Purchase #5	$76.78	7.599%	$82.6145	$82.61	$82.60	$82.60
Purchase #6	$72.85	12.783%	$82.1624	$82.16	$82.15	$82.20
Purchase #7	$100.29	11.517%	$111.8404	$111.84	$111.85	$111.80
7 purchase totals =	$927.13		$1,003.9700	$1,003.96	$1,003.95	$1,003.90