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	$26.94	3.123%	$27.7813	$27.78	$27.80	$27.80
Purchase #2	$31.77	5.628%	$33.558	$33.56	$33.55	$33.60
Purchase #3	$225.91	4.174%	$235.3395	$235.34	$235.35	$235.30
Purchase #4	$219.53	13.432%	$249.0173	$249.02	$249.00	$249.00
Purchase #5	$54.45	5.666%	$57.5351	$57.54	$57.55	$57.50
Purchase #6	$35.55	11.211%	$39.5355	$39.54	$39.55	$39.50
Purchase #7	$232.72	11.647%	$259.8249	$259.82	$259.80	$259.80
7 purchase totals =	$826.87		$902.5916	$902.60	$902.60	$902.50