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	$92.57	7.383%	$99.4044	$99.40	$99.40	$99.40
Purchase #2	$103.56	6.122%	$109.8999	$109.90	$109.90	$109.90
Purchase #3	$33.28	13.290%	$37.7029	$37.70	$37.70	$37.70
Purchase #4	$79.46	3.318%	$82.0965	$82.10	$82.10	$82.10
Purchase #5	$136.89	6.788%	$146.1821	$146.18	$146.20	$146.20
Purchase #6	$21.86	4.169%	$22.7713	$22.77	$22.75	$22.80
Purchase #7	$17.75	13.547%	$20.1546	$20.15	$20.15	$20.20
7 purchase totals =	$485.37		$518.2117	$518.20	$518.20	$518.30