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	$193.98	12.321%	$217.8803	$217.88	$217.90	$217.90
Purchase #2	$138.67	5.304%	$146.0251	$146.03	$146.05	$146.00
Purchase #3	$13.49	4.797%	$14.1371	$14.14	$14.15	$14.10
Purchase #4	$200.85	4.790%	$210.4707	$210.47	$210.45	$210.50
Purchase #5	$89.71	11.109%	$99.6759	$99.68	$99.70	$99.70
Purchase #6	$199.89	12.669%	$225.2141	$225.21	$225.20	$225.20
Purchase #7	$81.46	7.379%	$87.4709	$87.47	$87.45	$87.50
7 purchase totals =	$918.05		$1,000.8741	$1,000.88	$1,000.90	$1,000.90