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	$16.63	5.405%	$17.5289	$17.53	$17.55	$17.50
Purchase #2	$152.37	8.620%	$165.5043	$165.50	$165.50	$165.50
Purchase #3	$16.35	11.587%	$18.2445	$18.24	$18.25	$18.20
Purchase #4	$44.28	13.465%	$50.2423	$50.24	$50.25	$50.20
Purchase #5	$89.72	12.261%	$100.7206	$100.72	$100.70	$100.70
Purchase #6	$65.92	3.661%	$68.3333	$68.33	$68.35	$68.30
Purchase #7	$185.61	4.864%	$194.6381	$194.64	$194.65	$194.60
7 purchase totals =	$570.88		$615.2120	$615.20	$615.25	$615.00