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	$208.84	3.852%	$216.8845	$216.88	$216.90	$216.90
Purchase #2	$39.87	5.648%	$42.1219	$42.12	$42.10	$42.10
Purchase #3	$110.61	6.455%	$117.7499	$117.75	$117.75	$117.70
Purchase #4	$179.92	12.467%	$202.3506	$202.35	$202.35	$202.40
Purchase #5	$148.47	3.545%	$153.7333	$153.73	$153.75	$153.70
Purchase #6	$79.90	12.654%	$90.0105	$90.01	$90.00	$90.00
Purchase #7	$81.55	10.294%	$89.9448	$89.94	$89.95	$89.90
7 purchase totals =	$849.16		$912.7955	$912.78	$912.80	$912.70