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	$29.67	10.844%	$32.8874	$32.89	$32.90	$32.90
Purchase #2	$18.74	11.193%	$20.8376	$20.84	$20.85	$20.80
Purchase #3	$109.50	8.773%	$119.1064	$119.11	$119.10	$119.10
Purchase #4	$111.29	13.106%	$125.8757	$125.88	$125.90	$125.90
Purchase #5	$128.56	5.492%	$135.6205	$135.62	$135.60	$135.60
Purchase #6	$153.59	9.763%	$168.585	$168.59	$168.60	$168.60
Purchase #7	$87.51	3.489%	$90.5632	$90.56	$90.55	$90.60
7 purchase totals =	$638.86		$693.4758	$693.49	$693.50	$693.50