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	$39.84	6.336%	$42.3643	$42.36	$42.35	$42.40
Purchase #2	$38.48	9.110%	$41.9855	$41.99	$42.00	$42.00
Purchase #3	$179.91	4.670%	$188.3118	$188.31	$188.30	$188.30
Purchase #4	$172.34	12.820%	$194.434	$194.43	$194.45	$194.40
Purchase #5	$143.79	7.851%	$155.079	$155.08	$155.10	$155.10
Purchase #6	$74.47	9.528%	$81.5655	$81.57	$81.55	$81.60
Purchase #7	$56.78	10.547%	$62.7686	$62.77	$62.75	$62.80
7 purchase totals =	$705.61		$766.5087	$766.51	$766.50	$766.60