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	$128.33	13.298%	$145.3953	$145.40	$145.40	$145.40
Purchase #2	$210.79	6.146%	$223.7452	$223.75	$223.75	$223.70
Purchase #3	$85.91	8.638%	$93.3309	$93.33	$93.35	$93.30
Purchase #4	$213.71	12.870%	$241.2145	$241.21	$241.20	$241.20
Purchase #5	$153.81	3.570%	$159.301	$159.30	$159.30	$159.30
Purchase #6	$38.90	4.286%	$40.5673	$40.57	$40.55	$40.60
Purchase #7	$92.82	7.403%	$99.6915	$99.69	$99.70	$99.70
7 purchase totals =	$924.27		$1,003.2457	$1,003.25	$1,003.25	$1,003.20