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	$233.45	13.634%	$265.2786	$265.28	$265.30	$265.30
Purchase #2	$135.46	3.223%	$139.8259	$139.83	$139.85	$139.80
Purchase #3	$121.56	13.749%	$138.2733	$138.27	$138.25	$138.30
Purchase #4	$39.42	6.443%	$41.9598	$41.96	$41.95	$42.00
Purchase #5	$100.54	10.846%	$111.4446	$111.44	$111.45	$111.40
Purchase #6	$182.33	8.748%	$198.2802	$198.28	$198.30	$198.30
Purchase #7	$43.41	9.111%	$47.3651	$47.37	$47.35	$47.40
7 purchase totals =	$856.17		$942.4275	$942.43	$942.45	$942.50