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	$146.57	6.336%	$155.8567	$155.86	$155.85	$155.90
Purchase #2	$169.86	7.711%	$182.9579	$182.96	$182.95	$183.00
Purchase #3	$23.65	9.551%	$25.9088	$25.91	$25.90	$25.90
Purchase #4	$41.53	13.459%	$47.1195	$47.12	$47.10	$47.10
Purchase #5	$166.86	13.240%	$188.9523	$188.95	$188.95	$189.00
Purchase #6	$86.43	3.429%	$89.3937	$89.39	$89.40	$89.40
Purchase #7	$37.94	3.283%	$39.1856	$39.19	$39.20	$39.20
7 purchase totals =	$672.84		$729.3745	$729.38	$729.35	$729.50