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	$235.59	6.814%	$251.6431	$251.64	$251.65	$251.60
Purchase #2	$98.49	5.405%	$103.8134	$103.81	$103.80	$103.80
Purchase #3	$67.41	7.442%	$72.4267	$72.43	$72.45	$72.40
Purchase #4	$117.61	11.866%	$131.5656	$131.57	$131.55	$131.60
Purchase #5	$35.80	13.821%	$40.7479	$40.75	$40.75	$40.70
Purchase #6	$113.27	4.554%	$118.4283	$118.43	$118.45	$118.40
Purchase #7	$85.50	9.534%	$93.6516	$93.65	$93.65	$93.70
7 purchase totals =	$753.67		$812.2766	$812.28	$812.30	$812.20