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	$47.62	6.257%	$50.5996	$50.60	$50.60	$50.60
Purchase #2	$127.84	11.556%	$142.6132	$142.61	$142.60	$142.60
Purchase #3	$34.69	8.764%	$37.7302	$37.73	$37.75	$37.70
Purchase #4	$229.54	13.760%	$261.1247	$261.12	$261.10	$261.10
Purchase #5	$203.43	11.376%	$226.5722	$226.57	$226.55	$226.60
Purchase #6	$43.33	11.222%	$48.1925	$48.19	$48.20	$48.20
Purchase #7	$17.52	3.262%	$18.0915	$18.09	$18.10	$18.10
7 purchase totals =	$703.97		$784.9239	$784.91	$784.90	$784.90