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	$28.83	6.855%	$30.8063	$30.81	$30.80	$30.80
Purchase #2	$219.85	6.802%	$234.8042	$234.80	$234.80	$234.80
Purchase #3	$149.40	4.107%	$155.5359	$155.54	$155.55	$155.50
Purchase #4	$86.37	3.511%	$89.4025	$89.40	$89.40	$89.40
Purchase #5	$177.41	4.722%	$185.7873	$185.79	$185.80	$185.80
Purchase #6	$29.60	9.643%	$32.4543	$32.45	$32.45	$32.50
Purchase #7	$86.96	9.780%	$95.4647	$95.46	$95.45	$95.50
7 purchase totals =	$778.42		$824.2552	$824.25	$824.25	$824.30