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	$78.50	12.509%	$88.3196	$88.32	$88.30	$88.30
Purchase #2	$190.44	6.777%	$203.3461	$203.35	$203.35	$203.30
Purchase #3	$82.96	4.601%	$86.777	$86.78	$86.80	$86.80
Purchase #4	$103.98	11.621%	$116.0635	$116.06	$116.05	$116.10
Purchase #5	$81.41	12.549%	$91.6261	$91.63	$91.65	$91.60
Purchase #6	$51.73	5.283%	$54.4629	$54.46	$54.45	$54.50
Purchase #7	$29.47	12.434%	$33.1343	$33.13	$33.15	$33.10
7 purchase totals =	$618.49		$673.7295	$673.73	$673.75	$673.70