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	$161.82	4.173%	$168.5727	$168.57	$168.55	$168.60
Purchase #2	$237.47	10.805%	$263.1286	$263.13	$263.15	$263.10
Purchase #3	$37.50	13.670%	$42.6263	$42.63	$42.65	$42.60
Purchase #4	$18.69	11.815%	$20.8982	$20.90	$20.90	$20.90
Purchase #5	$250.30	5.597%	$264.3093	$264.31	$264.30	$264.30
Purchase #6	$104.28	12.508%	$117.3233	$117.32	$117.30	$117.30
Purchase #7	$92.52	12.779%	$104.3431	$104.34	$104.35	$104.30
7 purchase totals =	$902.58		$981.2015	$981.20	$981.20	$981.10