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	$224.82	3.510%	$232.7112	$232.71	$232.70	$232.70
Purchase #2	$90.43	8.678%	$98.2775	$98.28	$98.30	$98.30
Purchase #3	$60.52	9.835%	$66.4721	$66.47	$66.45	$66.50
Purchase #4	$97.97	7.128%	$104.9533	$104.95	$104.95	$105.00
Purchase #5	$88.40	13.123%	$100.0007	$100.00	$100.00	$100.00
Purchase #6	$37.72	9.609%	$41.3445	$41.34	$41.35	$41.30
Purchase #7	$181.90	4.228%	$189.5907	$189.59	$189.60	$189.60
7 purchase totals =	$781.76		$833.3500	$833.34	$833.35	$833.40