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	$17.92	12.805%	$20.2147	$20.21	$20.20	$20.20
Purchase #2	$162.25	13.112%	$183.5242	$183.52	$183.50	$183.50
Purchase #3	$37.32	3.116%	$38.4829	$38.48	$38.50	$38.50
Purchase #4	$218.73	3.468%	$226.3156	$226.32	$226.30	$226.30
Purchase #5	$37.77	12.797%	$42.6034	$42.60	$42.60	$42.60
Purchase #6	$134.92	11.768%	$150.7974	$150.80	$150.80	$150.80
Purchase #7	$90.47	6.232%	$96.1081	$96.11	$96.10	$96.10
7 purchase totals =	$699.38		$758.0463	$758.04	$758.00	$758.00