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	$55.86	6.245%	$59.3485	$59.35	$59.35	$59.30
Purchase #2	$165.91	3.759%	$172.1466	$172.15	$172.15	$172.10
Purchase #3	$92.85	8.342%	$100.5955	$100.60	$100.60	$100.60
Purchase #4	$147.56	10.302%	$162.7616	$162.76	$162.75	$162.80
Purchase #5	$217.66	12.791%	$245.5009	$245.50	$245.50	$245.50
Purchase #6	$138.91	11.799%	$155.3	$155.30	$155.30	$155.30
Purchase #7	$59.39	5.530%	$62.6743	$62.67	$62.65	$62.70
7 purchase totals =	$878.14		$958.3274	$958.33	$958.30	$958.30