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	$63.68	5.364%	$67.0958	$67.10	$67.10	$67.10
Purchase #2	$162.82	11.745%	$181.9432	$181.94	$181.95	$181.90
Purchase #3	$35.81	6.476%	$38.1291	$38.13	$38.15	$38.10
Purchase #4	$7.53	13.116%	$8.5176	$8.52	$8.50	$8.50
Purchase #5	$122.33	13.132%	$138.3944	$138.39	$138.40	$138.40
Purchase #6	$175.89	13.321%	$199.3203	$199.32	$199.30	$199.30
Purchase #7	$28.56	3.674%	$29.6093	$29.61	$29.60	$29.60
7 purchase totals =	$596.62		$663.0097	$663.01	$663.00	$662.90