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	$36.71	11.102%	$40.7855	$40.79	$40.80	$40.80
Purchase #2	$174.88	5.596%	$184.6663	$184.67	$184.65	$184.70
Purchase #3	$189.81	7.725%	$204.4728	$204.47	$204.45	$204.50
Purchase #4	$243.47	12.303%	$273.4241	$273.42	$273.40	$273.40
Purchase #5	$147.56	13.180%	$167.0084	$167.01	$167.00	$167.00
Purchase #6	$66.31	11.437%	$73.8939	$73.89	$73.90	$73.90
Purchase #7	$69.49	7.601%	$74.7719	$74.77	$74.75	$74.80
7 purchase totals =	$928.23		$1,019.0229	$1,019.02	$1,018.95	$1,019.10