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	$137.33	13.390%	$155.7185	$155.72	$155.70	$155.70
Purchase #2	$84.55	7.477%	$90.8718	$90.87	$90.85	$90.90
Purchase #3	$198.42	5.782%	$209.8926	$209.89	$209.90	$209.90
Purchase #4	$240.30	7.412%	$258.111	$258.11	$258.10	$258.10
Purchase #5	$207.82	7.830%	$224.0923	$224.09	$224.10	$224.10
Purchase #6	$229.59	12.145%	$257.4737	$257.47	$257.45	$257.50
Purchase #7	$48.86	8.315%	$52.9227	$52.92	$52.90	$52.90
7 purchase totals =	$1,146.87		$1,249.0826	$1,249.07	$1,249.00	$1,249.10