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	$198.87	12.792%	$224.3095	$224.31	$224.30	$224.30
Purchase #2	$227.86	6.348%	$242.3246	$242.32	$242.30	$242.30
Purchase #3	$214.38	12.720%	$241.6491	$241.65	$241.65	$241.60
Purchase #4	$217.77	13.314%	$246.7639	$246.76	$246.75	$246.80
Purchase #5	$35.50	11.264%	$39.4987	$39.50	$39.50	$39.50
Purchase #6	$178.69	6.754%	$190.7587	$190.76	$190.75	$190.80
Purchase #7	$101.79	7.247%	$109.1667	$109.17	$109.15	$109.20
7 purchase totals =	$1,174.86		$1,294.4712	$1,294.47	$1,294.40	$1,294.50