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	$90.48	12.188%	$101.5077	$101.51	$101.50	$101.50
Purchase #2	$61.92	11.186%	$68.8464	$68.85	$68.85	$68.80
Purchase #3	$57.39	3.154%	$59.2001	$59.20	$59.20	$59.20
Purchase #4	$139.77	8.247%	$151.2968	$151.30	$151.30	$151.30
Purchase #5	$125.80	4.805%	$131.8447	$131.84	$131.85	$131.80
Purchase #6	$119.59	13.627%	$135.8865	$135.89	$135.90	$135.90
Purchase #7	$246.64	9.649%	$270.4383	$270.44	$270.45	$270.40
7 purchase totals =	$841.59		$919.0205	$919.03	$919.05	$918.90