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	$97.60	6.818%	$104.2544	$104.25	$104.25	$104.30
Purchase #2	$116.89	3.400%	$120.8643	$120.86	$120.85	$120.90
Purchase #3	$160.83	4.537%	$168.1269	$168.13	$168.15	$168.10
Purchase #4	$135.60	12.720%	$152.8483	$152.85	$152.85	$152.80
Purchase #5	$28.78	3.561%	$29.8049	$29.80	$29.80	$29.80
Purchase #6	$33.27	10.333%	$36.7078	$36.71	$36.70	$36.70
Purchase #7	$89.90	10.418%	$99.2658	$99.27	$99.25	$99.30
7 purchase totals =	$662.87		$711.8724	$711.87	$711.85	$711.90