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	$115.92	9.823%	$127.3068	$127.31	$127.30	$127.30
Purchase #2	$203.42	12.177%	$228.1905	$228.19	$228.20	$228.20
Purchase #3	$150.41	3.719%	$156.0037	$156.00	$156.00	$156.00
Purchase #4	$99.50	12.438%	$111.8758	$111.88	$111.90	$111.90
Purchase #5	$156.28	7.779%	$168.437	$168.44	$168.45	$168.40
Purchase #6	$36.53	13.701%	$41.535	$41.54	$41.55	$41.50
Purchase #7	$146.34	3.689%	$151.7385	$151.74	$151.75	$151.70
7 purchase totals =	$908.40		$985.0873	$985.10	$985.15	$985.00