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	$242.78	5.738%	$256.7107	$256.71	$256.70	$256.70
Purchase #2	$53.87	6.245%	$57.2342	$57.23	$57.25	$57.20
Purchase #3	$234.82	4.607%	$245.6382	$245.64	$245.65	$245.60
Purchase #4	$80.59	10.854%	$89.3372	$89.34	$89.35	$89.30
Purchase #5	$92.80	6.636%	$98.9582	$98.96	$98.95	$99.00
Purchase #6	$202.71	12.714%	$228.4825	$228.48	$228.50	$228.50
Purchase #7	$163.66	4.415%	$170.8856	$170.89	$170.90	$170.90
7 purchase totals =	$1,071.23		$1,147.2466	$1,147.25	$1,147.30	$1,147.20