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	$39.92	4.761%	$41.8206	$41.82	$41.80	$41.80
Purchase #2	$200.79	4.645%	$210.1167	$210.12	$210.10	$210.10
Purchase #3	$84.42	7.195%	$90.494	$90.49	$90.50	$90.50
Purchase #4	$160.72	3.168%	$165.8116	$165.81	$165.80	$165.80
Purchase #5	$68.57	5.747%	$72.5107	$72.51	$72.50	$72.50
Purchase #6	$225.26	4.480%	$235.3516	$235.35	$235.35	$235.40
Purchase #7	$79.52	4.141%	$82.8129	$82.81	$82.80	$82.80
7 purchase totals =	$859.20		$898.9181	$898.91	$898.85	$898.90