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	$11.35	9.367%	$12.4132	$12.41	$12.40	$12.40
Purchase #2	$131.84	8.245%	$142.7102	$142.71	$142.70	$142.70
Purchase #3	$128.59	8.825%	$139.9381	$139.94	$139.95	$139.90
Purchase #4	$102.52	6.585%	$109.2709	$109.27	$109.25	$109.30
Purchase #5	$160.34	5.198%	$168.6745	$168.67	$168.65	$168.70
Purchase #6	$76.83	7.254%	$82.4032	$82.40	$82.40	$82.40
Purchase #7	$181.33	6.274%	$192.7066	$192.71	$192.70	$192.70
7 purchase totals =	$792.80		$848.1167	$848.11	$848.05	$848.10