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	$7.29	8.346%	$7.8984	$7.90	$7.90	$7.90
Purchase #2	$79.27	4.259%	$82.6461	$82.65	$82.65	$82.60
Purchase #3	$44.80	4.457%	$46.7967	$46.80	$46.80	$46.80
Purchase #4	$132.28	9.223%	$144.4802	$144.48	$144.50	$144.50
Purchase #5	$178.54	6.791%	$190.6647	$190.66	$190.65	$190.70
Purchase #6	$145.72	6.279%	$154.8698	$154.87	$154.85	$154.90
Purchase #7	$144.63	5.444%	$152.5037	$152.50	$152.50	$152.50
7 purchase totals =	$732.53		$779.8596	$779.86	$779.85	$779.90