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	$65.42	12.766%	$73.7715	$73.77	$73.75	$73.80
Purchase #2	$126.83	11.799%	$141.7947	$141.79	$141.80	$141.80
Purchase #3	$6.26	8.263%	$6.7773	$6.78	$6.80	$6.80
Purchase #4	$208.87	13.607%	$237.2909	$237.29	$237.30	$237.30
Purchase #5	$111.69	7.361%	$119.9115	$119.91	$119.90	$119.90
Purchase #6	$99.95	11.327%	$111.2713	$111.27	$111.25	$111.30
Purchase #7	$85.61	7.617%	$92.1309	$92.13	$92.15	$92.10
7 purchase totals =	$704.63		$782.9481	$782.94	$782.95	$783.00