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	$84.98	9.494%	$93.048	$93.05	$93.05	$93.00
Purchase #2	$175.43	8.695%	$190.6836	$190.68	$190.70	$190.70
Purchase #3	$196.95	9.300%	$215.2664	$215.27	$215.25	$215.30
Purchase #4	$200.77	7.517%	$215.8619	$215.86	$215.85	$215.90
Purchase #5	$93.29	11.112%	$103.6564	$103.66	$103.65	$103.70
Purchase #6	$28.72	10.105%	$31.6222	$31.62	$31.60	$31.60
Purchase #7	$116.70	12.870%	$131.7193	$131.72	$131.70	$131.70
7 purchase totals =	$896.84		$981.8578	$981.86	$981.80	$981.90