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	$53.72	11.452%	$59.872	$59.87	$59.85	$59.90
Purchase #2	$210.69	11.249%	$234.3905	$234.39	$234.40	$234.40
Purchase #3	$126.48	6.790%	$135.068	$135.07	$135.05	$135.10
Purchase #4	$38.81	4.467%	$40.5436	$40.54	$40.55	$40.50
Purchase #5	$121.59	10.314%	$134.1308	$134.13	$134.15	$134.10
Purchase #6	$52.55	12.760%	$59.2554	$59.26	$59.25	$59.30
Purchase #7	$235.76	13.728%	$268.1251	$268.13	$268.15	$268.10
7 purchase totals =	$839.60		$931.3854	$931.39	$931.40	$931.40