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	$36.51	4.711%	$38.23	$38.23	$38.25	$38.20
Purchase #2	$28.32	11.103%	$31.4644	$31.46	$31.45	$31.50
Purchase #3	$6.48	4.389%	$6.7644	$6.76	$6.75	$6.80
Purchase #4	$217.84	6.431%	$231.8493	$231.85	$231.85	$231.80
Purchase #5	$136.76	4.864%	$143.412	$143.41	$143.40	$143.40
Purchase #6	$85.30	3.555%	$88.3324	$88.33	$88.35	$88.30
Purchase #7	$200.88	3.669%	$208.2503	$208.25	$208.25	$208.30
7 purchase totals =	$712.09		$748.3028	$748.29	$748.30	$748.30