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	$25.92	7.658%	$27.905	$27.91	$27.90	$27.90
Purchase #2	$92.25	3.565%	$95.5387	$95.54	$95.55	$95.50
Purchase #3	$78.57	12.371%	$88.2899	$88.29	$88.30	$88.30
Purchase #4	$203.82	11.443%	$227.1431	$227.14	$227.15	$227.10
Purchase #5	$129.88	3.110%	$133.9193	$133.92	$133.90	$133.90
Purchase #6	$149.50	7.606%	$160.871	$160.87	$160.85	$160.90
Purchase #7	$44.94	12.615%	$50.6092	$50.61	$50.60	$50.60
7 purchase totals =	$724.88		$784.2762	$784.28	$784.25	$784.20