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	$52.84	4.702%	$55.3245	$55.32	$55.30	$55.30
Purchase #2	$133.99	4.379%	$139.8574	$139.86	$139.85	$139.90
Purchase #3	$113.59	8.618%	$123.3792	$123.38	$123.40	$123.40
Purchase #4	$200.95	3.793%	$208.572	$208.57	$208.55	$208.60
Purchase #5	$196.33	6.690%	$209.4645	$209.46	$209.45	$209.50
Purchase #6	$124.49	11.452%	$138.7466	$138.75	$138.75	$138.70
Purchase #7	$113.84	13.110%	$128.7644	$128.76	$128.75	$128.80
7 purchase totals =	$936.03		$1,004.1086	$1,004.10	$1,004.05	$1,004.20