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	$98.27	8.157%	$106.2859	$106.29	$106.30	$106.30
Purchase #2	$47.54	13.406%	$53.9132	$53.91	$53.90	$53.90
Purchase #3	$220.33	12.473%	$247.8118	$247.81	$247.80	$247.80
Purchase #4	$52.45	8.359%	$56.8343	$56.83	$56.85	$56.80
Purchase #5	$79.33	4.340%	$82.7729	$82.77	$82.75	$82.80
Purchase #6	$87.35	6.359%	$92.9046	$92.90	$92.90	$92.90
Purchase #7	$154.30	7.542%	$165.9373	$165.94	$165.95	$165.90
7 purchase totals =	$739.57		$806.4600	$806.45	$806.45	$806.40