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	$5.83	7.374%	$6.2599	$6.26	$6.25	$6.30
Purchase #2	$55.37	10.650%	$61.2669	$61.27	$61.25	$61.30
Purchase #3	$87.99	12.828%	$99.2774	$99.28	$99.30	$99.30
Purchase #4	$227.87	12.121%	$255.4901	$255.49	$255.50	$255.50
Purchase #5	$12.52	11.437%	$13.9519	$13.95	$13.95	$14.00
Purchase #6	$178.72	6.374%	$190.1116	$190.11	$190.10	$190.10
Purchase #7	$61.35	9.239%	$67.0181	$67.02	$67.00	$67.00
7 purchase totals =	$629.65		$693.3759	$693.38	$693.35	$693.50