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	$18.32	11.426%	$20.4132	$20.41	$20.40	$20.40
Purchase #2	$133.52	10.436%	$147.4541	$147.45	$147.45	$147.50
Purchase #3	$90.54	6.310%	$96.2531	$96.25	$96.25	$96.30
Purchase #4	$18.84	11.596%	$21.0247	$21.02	$21.00	$21.00
Purchase #5	$59.25	10.445%	$65.4387	$65.44	$65.45	$65.40
Purchase #6	$127.77	3.621%	$132.3966	$132.40	$132.40	$132.40
Purchase #7	$150.25	3.200%	$155.058	$155.06	$155.05	$155.10
7 purchase totals =	$598.49		$638.0384	$638.03	$638.00	$638.10