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	$32.97	9.165%	$35.9917	$35.99	$36.00	$36.00
Purchase #2	$131.66	6.397%	$140.0823	$140.08	$140.10	$140.10
Purchase #3	$38.48	10.334%	$42.4565	$42.46	$42.45	$42.50
Purchase #4	$99.41	10.398%	$109.7467	$109.75	$109.75	$109.70
Purchase #5	$154.51	8.198%	$167.1767	$167.18	$167.20	$167.20
Purchase #6	$63.51	12.639%	$71.537	$71.54	$71.55	$71.50
Purchase #7	$44.44	13.834%	$50.5878	$50.59	$50.60	$50.60
7 purchase totals =	$564.98		$617.5787	$617.59	$617.65	$617.60