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	$39.73	6.195%	$42.1913	$42.19	$42.20	$42.20
Purchase #2	$218.79	10.252%	$241.2204	$241.22	$241.20	$241.20
Purchase #3	$79.68	9.280%	$87.0743	$87.07	$87.05	$87.10
Purchase #4	$229.51	8.866%	$249.8584	$249.86	$249.85	$249.90
Purchase #5	$173.75	9.630%	$190.4821	$190.48	$190.50	$190.50
Purchase #6	$202.27	6.772%	$215.9677	$215.97	$215.95	$216.00
Purchase #7	$73.34	12.571%	$82.5596	$82.56	$82.55	$82.60
7 purchase totals =	$1,017.07		$1,109.3538	$1,109.35	$1,109.30	$1,109.50