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	$35.59	6.452%	$37.8863	$37.89	$37.90	$37.90
Purchase #2	$160.95	6.754%	$171.8206	$171.82	$171.80	$171.80
Purchase #3	$219.93	12.352%	$247.0958	$247.10	$247.10	$247.10
Purchase #4	$19.44	9.485%	$21.2839	$21.28	$21.30	$21.30
Purchase #5	$182.64	9.757%	$200.4602	$200.46	$200.45	$200.50
Purchase #6	$241.57	5.433%	$254.6945	$254.69	$254.70	$254.70
Purchase #7	$7.79	13.509%	$8.8424	$8.84	$8.85	$8.80
7 purchase totals =	$867.91		$942.0837	$942.08	$942.10	$942.10