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	$120.54	4.687%	$126.1897	$126.19	$126.20	$126.20
Purchase #2	$158.35	4.409%	$165.3317	$165.33	$165.35	$165.30
Purchase #3	$175.50	6.814%	$187.4586	$187.46	$187.45	$187.50
Purchase #4	$57.59	6.481%	$61.3224	$61.32	$61.30	$61.30
Purchase #5	$177.29	3.227%	$183.0111	$183.01	$183.00	$183.00
Purchase #6	$78.89	5.584%	$83.2952	$83.30	$83.30	$83.30
Purchase #7	$78.75	9.516%	$86.2439	$86.24	$86.25	$86.20
7 purchase totals =	$846.91		$892.8526	$892.85	$892.85	$892.80