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	$7.38	10.113%	$8.1263	$8.13	$8.15	$8.10
Purchase #2	$17.89	4.308%	$18.6607	$18.66	$18.65	$18.70
Purchase #3	$106.52	5.530%	$112.4106	$112.41	$112.40	$112.40
Purchase #4	$72.49	8.322%	$78.5226	$78.52	$78.50	$78.50
Purchase #5	$119.47	4.305%	$124.6132	$124.61	$124.60	$124.60
Purchase #6	$231.75	7.132%	$248.2784	$248.28	$248.30	$248.30
Purchase #7	$41.30	9.632%	$45.278	$45.28	$45.30	$45.30
7 purchase totals =	$596.80		$635.8898	$635.89	$635.90	$635.90