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	$79.25	9.488%	$86.7692	$86.77	$86.75	$86.80
Purchase #2	$100.27	8.801%	$109.0948	$109.09	$109.10	$109.10
Purchase #3	$249.98	12.492%	$281.2075	$281.21	$281.20	$281.20
Purchase #4	$41.30	13.483%	$46.8685	$46.87	$46.85	$46.90
Purchase #5	$154.80	10.552%	$171.1345	$171.13	$171.15	$171.10
Purchase #6	$40.56	12.120%	$45.4759	$45.48	$45.50	$45.50
Purchase #7	$130.34	11.133%	$144.8508	$144.85	$144.85	$144.90
7 purchase totals =	$796.50		$885.4012	$885.40	$885.40	$885.50