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	$81.78	10.442%	$90.3195	$90.32	$90.30	$90.30
Purchase #2	$62.53	8.188%	$67.65	$67.65	$67.65	$67.70
Purchase #3	$149.33	6.352%	$158.8154	$158.82	$158.80	$158.80
Purchase #4	$140.94	3.300%	$145.591	$145.59	$145.60	$145.60
Purchase #5	$198.46	13.848%	$225.9427	$225.94	$225.95	$225.90
Purchase #6	$201.63	10.352%	$222.5027	$222.50	$222.50	$222.50
Purchase #7	$213.36	13.582%	$242.3386	$242.34	$242.35	$242.30
7 purchase totals =	$1,048.03		$1,153.1599	$1,153.16	$1,153.15	$1,153.10