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	$151.66	12.828%	$171.1149	$171.11	$171.10	$171.10
Purchase #2	$72.42	8.748%	$78.7553	$78.76	$78.75	$78.80
Purchase #3	$224.27	13.541%	$254.6384	$254.64	$254.65	$254.60
Purchase #4	$89.79	4.222%	$93.5809	$93.58	$93.60	$93.60
Purchase #5	$114.93	7.703%	$123.7831	$123.78	$123.80	$123.80
Purchase #6	$110.51	5.234%	$116.2941	$116.29	$116.30	$116.30
Purchase #7	$213.69	8.365%	$231.5652	$231.57	$231.55	$231.60
7 purchase totals =	$977.27		$1,069.7319	$1,069.73	$1,069.75	$1,069.80