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	$240.67	12.318%	$270.3157	$270.32	$270.30	$270.30
Purchase #2	$38.29	9.811%	$42.0466	$42.05	$42.05	$42.00
Purchase #3	$156.28	5.554%	$164.9598	$164.96	$164.95	$165.00
Purchase #4	$134.41	7.238%	$144.1386	$144.14	$144.15	$144.10
Purchase #5	$187.92	12.505%	$211.4194	$211.42	$211.40	$211.40
Purchase #6	$9.52	13.770%	$10.8309	$10.83	$10.85	$10.80
Purchase #7	$174.58	9.577%	$191.2995	$191.30	$191.30	$191.30
7 purchase totals =	$941.67		$1,035.0105	$1,035.02	$1,035.00	$1,034.90