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	$164.75	6.207%	$174.976	$174.98	$175.00	$175.00
Purchase #2	$185.86	11.493%	$207.2209	$207.22	$207.20	$207.20
Purchase #3	$142.80	5.125%	$150.1185	$150.12	$150.10	$150.10
Purchase #4	$81.75	11.107%	$90.83	$90.83	$90.85	$90.80
Purchase #5	$89.35	3.375%	$92.3656	$92.37	$92.35	$92.40
Purchase #6	$18.83	8.750%	$20.4776	$20.48	$20.50	$20.50
Purchase #7	$124.90	4.782%	$130.8727	$130.87	$130.85	$130.90
7 purchase totals =	$808.24		$866.8613	$866.87	$866.85	$866.90