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	$21.55	10.263%	$23.7617	$23.76	$23.75	$23.80
Purchase #2	$77.85	7.801%	$83.9231	$83.92	$83.90	$83.90
Purchase #3	$231.73	7.424%	$248.9336	$248.93	$248.95	$248.90
Purchase #4	$56.57	10.788%	$62.6728	$62.67	$62.65	$62.70
Purchase #5	$197.43	13.816%	$224.7069	$224.71	$224.70	$224.70
Purchase #6	$171.33	5.678%	$181.0581	$181.06	$181.05	$181.10
Purchase #7	$246.80	11.610%	$275.4535	$275.45	$275.45	$275.50
7 purchase totals =	$1,003.26		$1,100.5097	$1,100.50	$1,100.45	$1,100.60