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	$35.69	3.328%	$36.8778	$36.88	$36.90	$36.90
Purchase #2	$51.30	9.695%	$56.2735	$56.27	$56.25	$56.30
Purchase #3	$150.34	12.531%	$169.1791	$169.18	$169.20	$169.20
Purchase #4	$191.47	7.372%	$205.5852	$205.59	$205.60	$205.60
Purchase #5	$102.33	8.611%	$111.1416	$111.14	$111.15	$111.10
Purchase #6	$100.38	11.386%	$111.8093	$111.81	$111.80	$111.80
Purchase #7	$97.45	7.850%	$105.0998	$105.10	$105.10	$105.10
7 purchase totals =	$728.96		$795.9663	$795.97	$796.00	$796.00