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	$29.78	8.474%	$32.3036	$32.30	$32.30	$32.30
Purchase #2	$215.91	12.485%	$242.8664	$242.87	$242.85	$242.90
Purchase #3	$119.29	12.524%	$134.2299	$134.23	$134.25	$134.20
Purchase #4	$90.98	6.215%	$96.6344	$96.63	$96.65	$96.60
Purchase #5	$35.72	5.522%	$37.6925	$37.69	$37.70	$37.70
Purchase #6	$176.97	7.723%	$190.6374	$190.64	$190.65	$190.60
Purchase #7	$51.50	5.128%	$54.1409	$54.14	$54.15	$54.10
7 purchase totals =	$720.15		$788.5051	$788.50	$788.55	$788.40