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	$240.27	10.448%	$265.3734	$265.37	$265.35	$265.40
Purchase #2	$40.63	5.568%	$42.8923	$42.89	$42.90	$42.90
Purchase #3	$193.25	9.313%	$211.2474	$211.25	$211.25	$211.20
Purchase #4	$12.98	10.691%	$14.3677	$14.37	$14.35	$14.40
Purchase #5	$30.79	10.140%	$33.9121	$33.91	$33.90	$33.90
Purchase #6	$105.51	9.360%	$115.3857	$115.39	$115.40	$115.40
Purchase #7	$121.60	8.218%	$131.5931	$131.59	$131.60	$131.60
7 purchase totals =	$745.03		$814.7717	$814.77	$814.75	$814.80