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	$105.71	3.618%	$109.5346	$109.53	$109.55	$109.50
Purchase #2	$74.25	5.483%	$78.3211	$78.32	$78.30	$78.30
Purchase #3	$81.52	6.553%	$86.862	$86.86	$86.85	$86.90
Purchase #4	$189.95	10.779%	$210.4247	$210.42	$210.40	$210.40
Purchase #5	$119.67	7.501%	$128.6464	$128.65	$128.65	$128.60
Purchase #6	$81.39	8.395%	$88.2227	$88.22	$88.20	$88.20
Purchase #7	$111.70	6.374%	$118.8198	$118.82	$118.80	$118.80
7 purchase totals =	$764.19		$820.8313	$820.82	$820.75	$820.70