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	$15.30	3.164%	$15.7841	$15.78	$15.80	$15.80
Purchase #2	$163.47	7.523%	$175.7678	$175.77	$175.75	$175.80
Purchase #3	$243.53	11.144%	$270.669	$270.67	$270.65	$270.70
Purchase #4	$30.78	3.580%	$31.8819	$31.88	$31.90	$31.90
Purchase #5	$117.26	5.364%	$123.5498	$123.55	$123.55	$123.50
Purchase #6	$171.71	11.185%	$190.9158	$190.92	$190.90	$190.90
Purchase #7	$90.85	4.802%	$95.2126	$95.21	$95.20	$95.20
7 purchase totals =	$832.90		$903.7810	$903.78	$903.75	$903.80