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	$70.55	11.277%	$78.5059	$78.51	$78.50	$78.50
Purchase #2	$71.44	9.700%	$78.3697	$78.37	$78.35	$78.40
Purchase #3	$110.65	8.527%	$120.0851	$120.09	$120.10	$120.10
Purchase #4	$179.96	9.231%	$196.5721	$196.57	$196.55	$196.60
Purchase #5	$106.45	12.755%	$120.0277	$120.03	$120.05	$120.00
Purchase #6	$98.58	5.474%	$103.9763	$103.98	$104.00	$104.00
Purchase #7	$86.25	5.602%	$91.0817	$91.08	$91.10	$91.10
7 purchase totals =	$723.88		$788.6185	$788.63	$788.65	$788.70