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	$219.39	5.505%	$231.4674	$231.47	$231.45	$231.50
Purchase #2	$223.89	4.170%	$233.2262	$233.23	$233.25	$233.20
Purchase #3	$200.40	11.283%	$223.0111	$223.01	$223.00	$223.00
Purchase #4	$109.35	7.834%	$117.9165	$117.92	$117.90	$117.90
Purchase #5	$7.41	13.861%	$8.4371	$8.44	$8.45	$8.40
Purchase #6	$47.81	4.282%	$49.8572	$49.86	$49.85	$49.90
Purchase #7	$82.92	4.587%	$86.7235	$86.72	$86.70	$86.70
7 purchase totals =	$891.17		$950.6390	$950.65	$950.60	$950.60