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	$104.31	3.654%	$108.1215	$108.12	$108.10	$108.10
Purchase #2	$183.43	3.750%	$190.3086	$190.31	$190.30	$190.30
Purchase #3	$79.77	4.504%	$83.3628	$83.36	$83.35	$83.40
Purchase #4	$89.82	12.215%	$100.7915	$100.79	$100.80	$100.80
Purchase #5	$75.80	8.869%	$82.5227	$82.52	$82.50	$82.50
Purchase #6	$199.70	11.543%	$222.7514	$222.75	$222.75	$222.80
Purchase #7	$126.68	11.705%	$141.5079	$141.51	$141.50	$141.50
7 purchase totals =	$859.51		$929.3664	$929.36	$929.30	$929.40