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	$155.36	4.591%	$162.4926	$162.49	$162.50	$162.50
Purchase #2	$159.38	4.860%	$167.1259	$167.13	$167.15	$167.10
Purchase #3	$246.28	7.243%	$264.1181	$264.12	$264.10	$264.10
Purchase #4	$70.27	3.458%	$72.6999	$72.70	$72.70	$72.70
Purchase #5	$105.71	10.642%	$116.9597	$116.96	$116.95	$117.00
Purchase #6	$92.90	5.111%	$97.6481	$97.65	$97.65	$97.60
Purchase #7	$112.94	3.459%	$116.8466	$116.85	$116.85	$116.80
7 purchase totals =	$942.84		$997.8909	$997.90	$997.90	$997.80