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	$73.71	7.480%	$79.2235	$79.22	$79.20	$79.20
Purchase #2	$241.73	8.397%	$262.0281	$262.03	$262.05	$262.00
Purchase #3	$171.45	10.444%	$189.3562	$189.36	$189.35	$189.40
Purchase #4	$34.54	9.730%	$37.9007	$37.90	$37.90	$37.90
Purchase #5	$96.59	13.667%	$109.791	$109.79	$109.80	$109.80
Purchase #6	$174.55	12.405%	$196.2029	$196.20	$196.20	$196.20
Purchase #7	$27.59	12.645%	$31.0788	$31.08	$31.10	$31.10
7 purchase totals =	$820.16		$905.5812	$905.58	$905.60	$905.60