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	$144.86	10.299%	$159.7791	$159.78	$159.80	$159.80
Purchase #2	$110.81	3.701%	$114.9111	$114.91	$114.90	$114.90
Purchase #3	$56.57	9.698%	$62.0562	$62.06	$62.05	$62.10
Purchase #4	$140.37	5.766%	$148.4637	$148.46	$148.45	$148.50
Purchase #5	$53.72	7.813%	$57.9171	$57.92	$57.90	$57.90
Purchase #6	$216.76	3.767%	$224.9253	$224.93	$224.95	$224.90
Purchase #7	$26.87	5.186%	$28.2635	$28.26	$28.25	$28.30
7 purchase totals =	$749.96		$796.3160	$796.32	$796.30	$796.40