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	$51.28	13.183%	$58.0402	$58.04	$58.05	$58.00
Purchase #2	$52.89	5.117%	$55.5964	$55.60	$55.60	$55.60
Purchase #3	$90.86	10.350%	$100.264	$100.26	$100.25	$100.30
Purchase #4	$39.74	5.681%	$41.9976	$42.00	$42.00	$42.00
Purchase #5	$182.35	11.609%	$203.519	$203.52	$203.50	$203.50
Purchase #6	$68.89	6.749%	$73.5394	$73.54	$73.55	$73.50
Purchase #7	$34.64	10.484%	$38.2717	$38.27	$38.25	$38.30
7 purchase totals =	$520.65		$571.2283	$571.23	$571.20	$571.20