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	$186.72	12.644%	$210.3289	$210.33	$210.35	$210.30
Purchase #2	$115.90	9.620%	$127.0496	$127.05	$127.05	$127.00
Purchase #3	$52.89	6.531%	$56.3442	$56.34	$56.35	$56.30
Purchase #4	$222.91	12.180%	$250.0604	$250.06	$250.05	$250.10
Purchase #5	$23.70	4.863%	$24.8525	$24.85	$24.85	$24.90
Purchase #6	$100.32	10.699%	$111.0532	$111.05	$111.05	$111.10
Purchase #7	$91.78	7.531%	$98.692	$98.69	$98.70	$98.70
7 purchase totals =	$794.22		$878.3808	$878.37	$878.40	$878.40