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	$226.32	4.810%	$237.206	$237.21	$237.20	$237.20
Purchase #2	$138.90	9.603%	$152.2386	$152.24	$152.25	$152.20
Purchase #3	$90.58	10.567%	$100.1516	$100.15	$100.15	$100.20
Purchase #4	$246.78	7.683%	$265.7401	$265.74	$265.75	$265.70
Purchase #5	$242.61	9.426%	$265.4784	$265.48	$265.50	$265.50
Purchase #6	$5.76	8.265%	$6.2361	$6.24	$6.25	$6.20
Purchase #7	$69.53	3.757%	$72.1422	$72.14	$72.15	$72.10
7 purchase totals =	$1,020.48		$1,099.1930	$1,099.20	$1,099.25	$1,099.10