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	$82.27	6.470%	$87.5929	$87.59	$87.60	$87.60
Purchase #2	$80.69	7.203%	$86.5021	$86.50	$86.50	$86.50
Purchase #3	$91.28	13.753%	$103.8337	$103.83	$103.85	$103.80
Purchase #4	$34.35	4.539%	$35.9091	$35.91	$35.90	$35.90
Purchase #5	$124.38	13.451%	$141.1104	$141.11	$141.10	$141.10
Purchase #6	$89.44	12.316%	$100.4554	$100.46	$100.45	$100.50
Purchase #7	$140.32	10.413%	$154.9315	$154.93	$154.95	$154.90
7 purchase totals =	$642.73		$710.3351	$710.33	$710.35	$710.30