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	$81.83	9.260%	$89.4075	$89.41	$89.40	$89.40
Purchase #2	$157.63	8.636%	$171.2429	$171.24	$171.25	$171.20
Purchase #3	$177.67	3.486%	$183.8636	$183.86	$183.85	$183.90
Purchase #4	$46.72	3.378%	$48.2982	$48.30	$48.30	$48.30
Purchase #5	$56.41	5.488%	$59.5058	$59.51	$59.50	$59.50
Purchase #6	$185.61	12.282%	$208.4066	$208.41	$208.40	$208.40
Purchase #7	$57.43	7.222%	$61.5776	$61.58	$61.60	$61.60
7 purchase totals =	$763.30		$822.3022	$822.31	$822.30	$822.30