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	$149.84	11.730%	$167.4162	$167.42	$167.40	$167.40
Purchase #2	$32.55	13.834%	$37.053	$37.05	$37.05	$37.10
Purchase #3	$202.91	3.789%	$210.5983	$210.60	$210.60	$210.60
Purchase #4	$222.89	3.791%	$231.3398	$231.34	$231.35	$231.30
Purchase #5	$68.26	6.732%	$72.8553	$72.86	$72.85	$72.90
Purchase #6	$173.50	6.280%	$184.3958	$184.40	$184.40	$184.40
Purchase #7	$26.43	6.612%	$28.1776	$28.18	$28.20	$28.20
7 purchase totals =	$876.38		$931.8360	$931.85	$931.85	$931.90