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	$76.47	7.835%	$82.4614	$82.46	$82.45	$82.50
Purchase #2	$172.30	3.318%	$178.0169	$178.02	$178.00	$178.00
Purchase #3	$177.94	10.288%	$196.2465	$196.25	$196.25	$196.20
Purchase #4	$196.96	11.851%	$220.3017	$220.30	$220.30	$220.30
Purchase #5	$238.62	13.199%	$270.1155	$270.12	$270.10	$270.10
Purchase #6	$87.77	4.391%	$91.624	$91.62	$91.60	$91.60
Purchase #7	$30.42	7.687%	$32.7584	$32.76	$32.75	$32.80
7 purchase totals =	$980.48		$1,071.5244	$1,071.53	$1,071.45	$1,071.50