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	$39.80	5.842%	$42.1251	$42.13	$42.15	$42.10
Purchase #2	$200.98	4.260%	$209.5417	$209.54	$209.55	$209.50
Purchase #3	$55.86	3.840%	$58.005	$58.01	$58.00	$58.00
Purchase #4	$166.99	11.550%	$186.2773	$186.28	$186.30	$186.30
Purchase #5	$18.30	11.704%	$20.4418	$20.44	$20.45	$20.40
Purchase #6	$211.56	3.756%	$219.5062	$219.51	$219.50	$219.50
Purchase #7	$244.29	13.579%	$277.4621	$277.46	$277.45	$277.50
7 purchase totals =	$937.78		$1,013.3592	$1,013.37	$1,013.40	$1,013.30