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	$135.98	9.256%	$148.5663	$148.57	$148.55	$148.60
Purchase #2	$17.59	11.544%	$19.6206	$19.62	$19.60	$19.60
Purchase #3	$146.87	12.127%	$164.6809	$164.68	$164.70	$164.70
Purchase #4	$242.59	13.710%	$275.8491	$275.85	$275.85	$275.80
Purchase #5	$13.33	10.196%	$14.6891	$14.69	$14.70	$14.70
Purchase #6	$119.52	3.700%	$123.9422	$123.94	$123.95	$123.90
Purchase #7	$73.78	13.816%	$83.9734	$83.97	$83.95	$84.00
7 purchase totals =	$749.66		$831.3216	$831.32	$831.30	$831.30