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	$96.37	12.196%	$108.1233	$108.12	$108.10	$108.10
Purchase #2	$134.89	7.381%	$144.8462	$144.85	$144.85	$144.80
Purchase #3	$220.59	12.540%	$248.252	$248.25	$248.25	$248.30
Purchase #4	$160.61	12.430%	$180.5738	$180.57	$180.55	$180.60
Purchase #5	$137.86	10.736%	$152.6606	$152.66	$152.65	$152.70
Purchase #6	$109.86	3.666%	$113.8875	$113.89	$113.90	$113.90
Purchase #7	$184.66	9.520%	$202.2396	$202.24	$202.25	$202.20
7 purchase totals =	$1,044.84		$1,150.5830	$1,150.58	$1,150.55	$1,150.60