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	$180.77	4.375%	$188.6787	$188.68	$188.70	$188.70
Purchase #2	$121.76	7.684%	$131.116	$131.12	$131.10	$131.10
Purchase #3	$40.86	6.742%	$43.6148	$43.61	$43.60	$43.60
Purchase #4	$140.78	3.525%	$145.7425	$145.74	$145.75	$145.70
Purchase #5	$83.40	7.461%	$89.6225	$89.62	$89.60	$89.60
Purchase #6	$76.87	6.488%	$81.8573	$81.86	$81.85	$81.90
Purchase #7	$58.34	5.356%	$61.4647	$61.46	$61.45	$61.50
7 purchase totals =	$702.78		$742.0965	$742.09	$742.05	$742.10