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	$168.39	9.560%	$184.4881	$184.49	$184.50	$184.50
Purchase #2	$101.86	10.110%	$112.158	$112.16	$112.15	$112.20
Purchase #3	$9.44	13.161%	$10.6824	$10.68	$10.70	$10.70
Purchase #4	$181.59	3.352%	$187.6769	$187.68	$187.70	$187.70
Purchase #5	$140.59	10.872%	$155.8749	$155.87	$155.85	$155.90
Purchase #6	$71.31	10.532%	$78.8204	$78.82	$78.80	$78.80
Purchase #7	$74.46	5.804%	$78.7817	$78.78	$78.80	$78.80
7 purchase totals =	$747.64		$808.4824	$808.48	$808.50	$808.60