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	$50.83	13.119%	$57.4984	$57.50	$57.50	$57.50
Purchase #2	$162.87	8.270%	$176.3393	$176.34	$176.35	$176.30
Purchase #3	$119.71	6.180%	$127.1081	$127.11	$127.10	$127.10
Purchase #4	$206.55	7.648%	$222.3469	$222.35	$222.35	$222.30
Purchase #5	$80.42	12.674%	$90.6124	$90.61	$90.60	$90.60
Purchase #6	$135.25	6.749%	$144.378	$144.38	$144.40	$144.40
Purchase #7	$77.58	9.573%	$85.0067	$85.01	$85.00	$85.00
7 purchase totals =	$833.21		$903.2898	$903.30	$903.30	$903.20