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	$36.98	9.591%	$40.5268	$40.53	$40.55	$40.50
Purchase #2	$36.37	11.349%	$40.4976	$40.50	$40.50	$40.50
Purchase #3	$20.67	9.193%	$22.5702	$22.57	$22.55	$22.60
Purchase #4	$236.72	5.564%	$249.8911	$249.89	$249.90	$249.90
Purchase #5	$67.40	7.744%	$72.6195	$72.62	$72.60	$72.60
Purchase #6	$87.88	13.135%	$99.423	$99.42	$99.40	$99.40
Purchase #7	$178.66	10.113%	$196.7279	$196.73	$196.75	$196.70
7 purchase totals =	$664.68		$722.2561	$722.26	$722.25	$722.20