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	$91.86	9.726%	$100.7943	$100.79	$100.80	$100.80
Purchase #2	$210.66	12.476%	$236.9419	$236.94	$236.95	$236.90
Purchase #3	$14.36	8.396%	$15.5657	$15.57	$15.55	$15.60
Purchase #4	$144.77	11.734%	$161.7573	$161.76	$161.75	$161.80
Purchase #5	$85.90	4.495%	$89.7612	$89.76	$89.75	$89.80
Purchase #6	$48.43	8.469%	$52.5315	$52.53	$52.55	$52.50
Purchase #7	$78.91	9.254%	$86.2123	$86.21	$86.20	$86.20
7 purchase totals =	$674.89		$743.5642	$743.56	$743.55	$743.60