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	$82.89	7.678%	$89.2543	$89.25	$89.25	$89.30
Purchase #2	$36.73	6.256%	$39.0278	$39.03	$39.05	$39.00
Purchase #3	$39.37	3.725%	$40.8365	$40.84	$40.85	$40.80
Purchase #4	$149.78	8.655%	$162.7435	$162.74	$162.75	$162.70
Purchase #5	$198.25	3.535%	$205.2581	$205.26	$205.25	$205.30
Purchase #6	$18.29	9.584%	$20.0429	$20.04	$20.05	$20.00
Purchase #7	$123.96	10.261%	$136.6795	$136.68	$136.70	$136.70
7 purchase totals =	$649.27		$693.8426	$693.84	$693.90	$693.80