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	$34.27	9.248%	$37.4393	$37.44	$37.45	$37.40
Purchase #2	$141.55	6.632%	$150.9376	$150.94	$150.95	$150.90
Purchase #3	$88.68	7.154%	$95.0242	$95.02	$95.00	$95.00
Purchase #4	$234.57	7.152%	$251.3464	$251.35	$251.35	$251.30
Purchase #5	$29.38	3.661%	$30.4556	$30.46	$30.45	$30.50
Purchase #6	$151.79	13.700%	$172.5852	$172.59	$172.60	$172.60
Purchase #7	$86.71	5.750%	$91.6958	$91.70	$91.70	$91.70
7 purchase totals =	$766.95		$829.4841	$829.50	$829.50	$829.40