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	$233.39	10.359%	$257.5669	$257.57	$257.55	$257.60
Purchase #2	$64.87	12.548%	$73.0099	$73.01	$73.00	$73.00
Purchase #3	$106.44	9.814%	$116.886	$116.89	$116.90	$116.90
Purchase #4	$161.94	7.300%	$173.7616	$173.76	$173.75	$173.80
Purchase #5	$112.73	13.414%	$127.8516	$127.85	$127.85	$127.90
Purchase #6	$53.37	4.200%	$55.6115	$55.61	$55.60	$55.60
Purchase #7	$48.89	7.627%	$52.6188	$52.62	$52.60	$52.60
7 purchase totals =	$781.63		$857.3063	$857.31	$857.25	$857.40