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	$46.39	5.630%	$49.0018	$49.00	$49.00	$49.00
Purchase #2	$154.29	7.772%	$166.2814	$166.28	$166.30	$166.30
Purchase #3	$71.89	9.586%	$78.7814	$78.78	$78.80	$78.80
Purchase #4	$95.70	5.606%	$101.0649	$101.06	$101.05	$101.10
Purchase #5	$45.52	11.402%	$50.7102	$50.71	$50.70	$50.70
Purchase #6	$62.51	3.872%	$64.9304	$64.93	$64.95	$64.90
Purchase #7	$25.81	6.608%	$27.5155	$27.52	$27.50	$27.50
7 purchase totals =	$502.11		$538.2856	$538.28	$538.30	$538.30