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	$90.56	10.553%	$100.1168	$100.12	$100.10	$100.10
Purchase #2	$37.41	12.362%	$42.0346	$42.03	$42.05	$42.00
Purchase #3	$182.92	11.285%	$203.5625	$203.56	$203.55	$203.60
Purchase #4	$247.74	3.439%	$256.2598	$256.26	$256.25	$256.30
Purchase #5	$204.47	7.719%	$220.253	$220.25	$220.25	$220.30
Purchase #6	$246.80	3.572%	$255.6157	$255.62	$255.60	$255.60
Purchase #7	$54.97	11.782%	$61.4466	$61.45	$61.45	$61.40
7 purchase totals =	$1,064.87		$1,139.2890	$1,139.29	$1,139.25	$1,139.30