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	$32.36	12.827%	$36.5108	$36.51	$36.50	$36.50
Purchase #2	$136.60	4.860%	$143.2388	$143.24	$143.25	$143.20
Purchase #3	$78.73	4.805%	$82.513	$82.51	$82.50	$82.50
Purchase #4	$77.90	11.520%	$86.8741	$86.87	$86.85	$86.90
Purchase #5	$236.45	5.134%	$248.5893	$248.59	$248.60	$248.60
Purchase #6	$44.95	7.425%	$48.2875	$48.29	$48.30	$48.30
Purchase #7	$173.44	6.539%	$184.7812	$184.78	$184.80	$184.80
7 purchase totals =	$780.43		$830.7947	$830.79	$830.80	$830.80