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	$48.64	8.866%	$52.9524	$52.95	$52.95	$53.00
Purchase #2	$156.52	9.184%	$170.8948	$170.89	$170.90	$170.90
Purchase #3	$95.98	5.385%	$101.1485	$101.15	$101.15	$101.10
Purchase #4	$56.30	10.425%	$62.1693	$62.17	$62.15	$62.20
Purchase #5	$29.86	8.442%	$32.3808	$32.38	$32.40	$32.40
Purchase #6	$131.53	7.804%	$141.7946	$141.79	$141.80	$141.80
Purchase #7	$81.27	3.159%	$83.8373	$83.84	$83.85	$83.80
7 purchase totals =	$600.10		$645.1777	$645.17	$645.20	$645.20