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	$187.53	6.374%	$199.4832	$199.48	$199.50	$199.50
Purchase #2	$161.31	4.345%	$168.3189	$168.32	$168.30	$168.30
Purchase #3	$35.39	13.124%	$40.0346	$40.03	$40.05	$40.00
Purchase #4	$88.71	11.701%	$99.09	$99.09	$99.10	$99.10
Purchase #5	$105.82	7.552%	$113.8115	$113.81	$113.80	$113.80
Purchase #6	$106.50	4.663%	$111.4661	$111.47	$111.45	$111.50
Purchase #7	$239.28	7.358%	$256.8862	$256.89	$256.90	$256.90
7 purchase totals =	$924.54		$989.0905	$989.09	$989.10	$989.10