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	$96.39	3.242%	$99.515	$99.52	$99.50	$99.50
Purchase #2	$141.87	13.418%	$160.9061	$160.91	$160.90	$160.90
Purchase #3	$110.46	6.107%	$117.2058	$117.21	$117.20	$117.20
Purchase #4	$135.94	12.407%	$152.8061	$152.81	$152.80	$152.80
Purchase #5	$242.81	5.723%	$256.706	$256.71	$256.70	$256.70
Purchase #6	$134.37	10.236%	$148.1241	$148.12	$148.10	$148.10
Purchase #7	$83.63	3.595%	$86.6365	$86.64	$86.65	$86.60
7 purchase totals =	$945.47		$1,021.8996	$1,021.92	$1,021.85	$1,021.80