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	$137.52	13.657%	$156.3011	$156.30	$156.30	$156.30
Purchase #2	$69.99	9.342%	$76.5285	$76.53	$76.55	$76.50
Purchase #3	$181.59	4.406%	$189.5909	$189.59	$189.60	$189.60
Purchase #4	$240.69	10.324%	$265.5388	$265.54	$265.55	$265.50
Purchase #5	$194.50	12.535%	$218.8806	$218.88	$218.90	$218.90
Purchase #6	$48.71	6.385%	$51.8201	$51.82	$51.80	$51.80
Purchase #7	$42.42	11.302%	$47.2143	$47.21	$47.20	$47.20
7 purchase totals =	$915.42		$1,005.8743	$1,005.87	$1,005.90	$1,005.80