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	$97.30	3.271%	$100.4827	$100.48	$100.50	$100.50
Purchase #2	$50.63	10.464%	$55.9279	$55.93	$55.95	$55.90
Purchase #3	$79.63	12.582%	$89.649	$89.65	$89.65	$89.60
Purchase #4	$247.69	7.772%	$266.9405	$266.94	$266.95	$266.90
Purchase #5	$133.58	12.766%	$150.6328	$150.63	$150.65	$150.60
Purchase #6	$178.65	6.254%	$189.8228	$189.82	$189.80	$189.80
Purchase #7	$90.41	9.191%	$98.7196	$98.72	$98.70	$98.70
7 purchase totals =	$877.89		$952.1753	$952.17	$952.20	$952.00