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	$108.29	10.712%	$119.89	$119.89	$119.90	$119.90
Purchase #2	$250.64	12.480%	$281.9199	$281.92	$281.90	$281.90
Purchase #3	$180.33	6.316%	$191.7196	$191.72	$191.70	$191.70
Purchase #4	$137.51	6.606%	$146.5939	$146.59	$146.60	$146.60
Purchase #5	$195.90	13.135%	$221.6315	$221.63	$221.65	$221.60
Purchase #6	$20.69	9.705%	$22.698	$22.70	$22.70	$22.70
Purchase #7	$202.30	6.532%	$215.5142	$215.51	$215.50	$215.50
7 purchase totals =	$1,095.66		$1,199.9671	$1,199.96	$1,199.95	$1,199.90