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	$82.73	8.693%	$89.9217	$89.92	$89.90	$89.90
Purchase #2	$150.83	9.632%	$165.3579	$165.36	$165.35	$165.40
Purchase #3	$6.45	9.238%	$7.0459	$7.05	$7.05	$7.00
Purchase #4	$226.51	10.411%	$250.092	$250.09	$250.10	$250.10
Purchase #5	$145.36	7.698%	$156.5498	$156.55	$156.55	$156.50
Purchase #6	$173.37	7.713%	$186.742	$186.74	$186.75	$186.70
Purchase #7	$87.27	7.752%	$94.0352	$94.04	$94.05	$94.00
7 purchase totals =	$872.52		$949.7445	$949.75	$949.75	$949.60