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	$125.38	9.520%	$137.3162	$137.32	$137.30	$137.30
Purchase #2	$148.76	9.127%	$162.3373	$162.34	$162.35	$162.30
Purchase #3	$85.31	6.141%	$90.5489	$90.55	$90.55	$90.50
Purchase #4	$140.57	12.825%	$158.5981	$158.60	$158.60	$158.60
Purchase #5	$39.56	9.642%	$43.3744	$43.37	$43.35	$43.40
Purchase #6	$112.96	4.681%	$118.2477	$118.25	$118.25	$118.20
Purchase #7	$11.25	13.568%	$12.7764	$12.78	$12.80	$12.80
7 purchase totals =	$663.79		$723.1990	$723.21	$723.20	$723.10