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	$48.33	10.427%	$53.3694	$53.37	$53.35	$53.40
Purchase #2	$55.88	12.484%	$62.8561	$62.86	$62.85	$62.90
Purchase #3	$56.38	8.622%	$61.2411	$61.24	$61.25	$61.20
Purchase #4	$47.71	5.389%	$50.2811	$50.28	$50.30	$50.30
Purchase #5	$120.82	11.767%	$135.0369	$135.04	$135.05	$135.00
Purchase #6	$56.47	6.162%	$59.9497	$59.95	$59.95	$59.90
Purchase #7	$155.46	5.857%	$164.5653	$164.57	$164.55	$164.60
7 purchase totals =	$541.05		$587.2996	$587.31	$587.30	$587.30