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	$64.93	9.661%	$71.2029	$71.20	$71.20	$71.20
Purchase #2	$75.89	8.610%	$82.4241	$82.42	$82.40	$82.40
Purchase #3	$241.31	10.599%	$266.8864	$266.89	$266.90	$266.90
Purchase #4	$61.49	4.858%	$64.4772	$64.48	$64.50	$64.50
Purchase #5	$145.31	9.315%	$158.8456	$158.85	$158.85	$158.80
Purchase #6	$67.77	6.850%	$72.4122	$72.41	$72.40	$72.40
Purchase #7	$198.31	12.272%	$222.6466	$222.65	$222.65	$222.60
7 purchase totals =	$855.01		$938.8950	$938.90	$938.90	$938.80