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	$103.32	13.821%	$117.5999	$117.60	$117.60	$117.60
Purchase #2	$202.25	4.672%	$211.6991	$211.70	$211.70	$211.70
Purchase #3	$98.85	4.368%	$103.1678	$103.17	$103.15	$103.20
Purchase #4	$64.33	13.285%	$72.8762	$72.88	$72.90	$72.90
Purchase #5	$61.94	4.306%	$64.6071	$64.61	$64.60	$64.60
Purchase #6	$212.64	12.614%	$239.4624	$239.46	$239.45	$239.50
Purchase #7	$151.54	11.714%	$169.2914	$169.29	$169.30	$169.30
7 purchase totals =	$894.87		$978.7039	$978.71	$978.70	$978.80