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	$83.88	4.307%	$87.4927	$87.49	$87.50	$87.50
Purchase #2	$232.29	13.669%	$264.0417	$264.04	$264.05	$264.00
Purchase #3	$243.93	12.385%	$274.1407	$274.14	$274.15	$274.10
Purchase #4	$86.61	5.250%	$91.157	$91.16	$91.15	$91.20
Purchase #5	$112.85	13.565%	$128.1581	$128.16	$128.15	$128.20
Purchase #6	$95.51	9.690%	$104.7649	$104.76	$104.75	$104.80
Purchase #7	$31.72	3.289%	$32.7633	$32.76	$32.75	$32.80
7 purchase totals =	$886.79		$982.5184	$982.51	$982.50	$982.60