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	$155.33	9.334%	$169.8285	$169.83	$169.85	$169.80
Purchase #2	$56.78	13.229%	$64.2914	$64.29	$64.30	$64.30
Purchase #3	$109.45	4.696%	$114.5898	$114.59	$114.60	$114.60
Purchase #4	$148.43	13.527%	$168.5081	$168.51	$168.50	$168.50
Purchase #5	$28.35	5.618%	$29.9427	$29.94	$29.95	$29.90
Purchase #6	$202.77	8.438%	$219.8797	$219.88	$219.90	$219.90
Purchase #7	$214.27	7.250%	$229.8046	$229.80	$229.80	$229.80
7 purchase totals =	$915.38		$996.8448	$996.84	$996.90	$996.80