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	$199.38	11.746%	$222.7992	$222.80	$222.80	$222.80
Purchase #2	$217.68	5.568%	$229.8004	$229.80	$229.80	$229.80
Purchase #3	$225.79	5.812%	$238.9129	$238.91	$238.90	$238.90
Purchase #4	$86.46	3.412%	$89.41	$89.41	$89.40	$89.40
Purchase #5	$95.35	7.216%	$102.2305	$102.23	$102.25	$102.20
Purchase #6	$116.32	12.406%	$130.7507	$130.75	$130.75	$130.80
Purchase #7	$229.98	13.609%	$261.278	$261.28	$261.30	$261.30
7 purchase totals =	$1,170.96		$1,275.1817	$1,275.18	$1,275.20	$1,275.20