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	$99.40	13.660%	$112.978	$112.98	$113.00	$113.00
Purchase #2	$142.84	6.286%	$151.8189	$151.82	$151.80	$151.80
Purchase #3	$55.96	12.249%	$62.8145	$62.81	$62.80	$62.80
Purchase #4	$149.37	8.696%	$162.3592	$162.36	$162.35	$162.40
Purchase #5	$28.61	3.321%	$29.5601	$29.56	$29.55	$29.60
Purchase #6	$189.61	11.265%	$210.9696	$210.97	$210.95	$211.00
Purchase #7	$102.56	8.697%	$111.4796	$111.48	$111.50	$111.50
7 purchase totals =	$768.35		$841.9799	$841.98	$841.95	$842.10