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	$243.63	11.760%	$272.2809	$272.28	$272.30	$272.30
Purchase #2	$226.41	7.628%	$243.6806	$243.68	$243.70	$243.70
Purchase #3	$82.50	10.287%	$90.9868	$90.99	$91.00	$91.00
Purchase #4	$105.70	3.387%	$109.2801	$109.28	$109.30	$109.30
Purchase #5	$46.59	4.781%	$48.8175	$48.82	$48.80	$48.80
Purchase #6	$82.51	3.382%	$85.3005	$85.30	$85.30	$85.30
Purchase #7	$91.30	9.801%	$100.2483	$100.25	$100.25	$100.20
7 purchase totals =	$878.64		$950.5947	$950.60	$950.65	$950.60