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	$29.82	6.115%	$31.6435	$31.64	$31.65	$31.60
Purchase #2	$54.87	7.457%	$58.9617	$58.96	$58.95	$59.00
Purchase #3	$48.59	11.748%	$54.2984	$54.30	$54.30	$54.30
Purchase #4	$190.50	13.109%	$215.4726	$215.47	$215.45	$215.50
Purchase #5	$131.40	8.441%	$142.4915	$142.49	$142.50	$142.50
Purchase #6	$138.30	4.375%	$144.3506	$144.35	$144.35	$144.40
Purchase #7	$168.38	7.590%	$181.16	$181.16	$181.15	$181.20
7 purchase totals =	$761.86		$828.3783	$828.37	$828.35	$828.50