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	$33.63	11.477%	$37.4897	$37.49	$37.50	$37.50
Purchase #2	$174.72	12.632%	$196.7906	$196.79	$196.80	$196.80
Purchase #3	$53.52	7.557%	$57.5645	$57.56	$57.55	$57.60
Purchase #4	$137.33	6.452%	$146.1905	$146.19	$146.20	$146.20
Purchase #5	$238.95	13.626%	$271.5093	$271.51	$271.50	$271.50
Purchase #6	$134.37	6.189%	$142.6862	$142.69	$142.70	$142.70
Purchase #7	$59.99	12.425%	$67.4438	$67.44	$67.45	$67.40
7 purchase totals =	$832.51		$919.6746	$919.67	$919.70	$919.70