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	$96.94	3.154%	$99.9975	$100.00	$100.00	$100.00
Purchase #2	$22.63	6.513%	$24.1039	$24.10	$24.10	$24.10
Purchase #3	$36.44	5.433%	$38.4198	$38.42	$38.40	$38.40
Purchase #4	$134.35	9.434%	$147.0246	$147.02	$147.00	$147.00
Purchase #5	$78.80	13.826%	$89.6949	$89.69	$89.70	$89.70
Purchase #6	$63.25	13.409%	$71.7312	$71.73	$71.75	$71.70
Purchase #7	$92.55	13.488%	$105.0331	$105.03	$105.05	$105.00
7 purchase totals =	$524.96		$576.0050	$575.99	$576.00	$575.90