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	$45.41	4.599%	$47.4984	$47.50	$47.50	$47.50
Purchase #2	$222.57	3.178%	$229.6433	$229.64	$229.65	$229.60
Purchase #3	$95.94	4.632%	$100.3839	$100.38	$100.40	$100.40
Purchase #4	$248.35	7.708%	$267.4928	$267.49	$267.50	$267.50
Purchase #5	$32.83	7.274%	$35.2181	$35.22	$35.20	$35.20
Purchase #6	$110.78	5.601%	$116.9848	$116.98	$117.00	$117.00
Purchase #7	$188.33	3.334%	$194.6089	$194.61	$194.60	$194.60
7 purchase totals =	$944.21		$991.8302	$991.82	$991.85	$991.80