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	$123.88	7.283%	$132.9022	$132.90	$132.90	$132.90
Purchase #2	$162.83	6.710%	$173.7559	$173.76	$173.75	$173.80
Purchase #3	$36.33	5.123%	$38.1912	$38.19	$38.20	$38.20
Purchase #4	$237.55	9.863%	$260.9796	$260.98	$261.00	$261.00
Purchase #5	$115.40	13.847%	$131.3794	$131.38	$131.40	$131.40
Purchase #6	$109.31	4.870%	$114.6334	$114.63	$114.65	$114.60
Purchase #7	$86.59	3.274%	$89.425	$89.43	$89.45	$89.40
7 purchase totals =	$871.89		$941.2667	$941.27	$941.35	$941.30