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	$218.61	11.551%	$243.8616	$243.86	$243.85	$243.90
Purchase #2	$151.55	7.304%	$162.6192	$162.62	$162.60	$162.60
Purchase #3	$103.68	6.512%	$110.4316	$110.43	$110.45	$110.40
Purchase #4	$62.83	3.292%	$64.8984	$64.90	$64.90	$64.90
Purchase #5	$82.38	10.437%	$90.978	$90.98	$91.00	$91.00
Purchase #6	$66.58	9.578%	$72.957	$72.96	$72.95	$73.00
Purchase #7	$222.96	4.605%	$233.2273	$233.23	$233.25	$233.20
7 purchase totals =	$908.59		$978.9731	$978.98	$979.00	$979.00