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	$58.41	5.824%	$61.8118	$61.81	$61.80	$61.80
Purchase #2	$100.49	11.853%	$112.4011	$112.40	$112.40	$112.40
Purchase #3	$156.42	7.718%	$168.4925	$168.49	$168.50	$168.50
Purchase #4	$131.52	5.239%	$138.4103	$138.41	$138.40	$138.40
Purchase #5	$83.83	12.755%	$94.5225	$94.52	$94.50	$94.50
Purchase #6	$172.33	13.463%	$195.5308	$195.53	$195.55	$195.50
Purchase #7	$49.82	7.665%	$53.6387	$53.64	$53.65	$53.60
7 purchase totals =	$752.82		$824.8077	$824.80	$824.80	$824.70