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	$213.30	11.777%	$238.4203	$238.42	$238.40	$238.40
Purchase #2	$156.85	4.686%	$164.2	$164.20	$164.20	$164.20
Purchase #3	$171.85	4.613%	$179.7774	$179.78	$179.80	$179.80
Purchase #4	$93.87	5.376%	$98.9165	$98.92	$98.90	$98.90
Purchase #5	$113.77	3.853%	$118.1536	$118.15	$118.15	$118.20
Purchase #6	$75.86	8.808%	$82.5417	$82.54	$82.55	$82.50
Purchase #7	$196.96	5.753%	$208.2911	$208.29	$208.30	$208.30
7 purchase totals =	$1,022.46		$1,090.3006	$1,090.30	$1,090.30	$1,090.30