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	$15.96	9.207%	$17.4294	$17.43	$17.45	$17.40
Purchase #2	$38.33	11.591%	$42.7728	$42.77	$42.75	$42.80
Purchase #3	$185.55	13.672%	$210.9184	$210.92	$210.90	$210.90
Purchase #4	$161.86	10.647%	$179.0932	$179.09	$179.10	$179.10
Purchase #5	$59.34	11.503%	$66.1659	$66.17	$66.15	$66.20
Purchase #6	$148.44	11.365%	$165.3102	$165.31	$165.30	$165.30
Purchase #7	$143.90	12.649%	$162.1019	$162.10	$162.10	$162.10
7 purchase totals =	$753.38		$843.7918	$843.79	$843.75	$843.80