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	$88.66	13.116%	$100.2886	$100.29	$100.30	$100.30
Purchase #2	$202.29	11.740%	$226.0388	$226.04	$226.05	$226.00
Purchase #3	$124.66	5.442%	$131.444	$131.44	$131.45	$131.40
Purchase #4	$223.47	7.783%	$240.8627	$240.86	$240.85	$240.90
Purchase #5	$20.35	5.554%	$21.4802	$21.48	$21.50	$21.50
Purchase #6	$153.72	8.852%	$167.3273	$167.33	$167.35	$167.30
Purchase #7	$212.65	7.401%	$228.3882	$228.39	$228.40	$228.40
7 purchase totals =	$1,025.80		$1,115.8298	$1,115.83	$1,115.90	$1,115.80