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	$25.88	5.688%	$27.3521	$27.35	$27.35	$27.40
Purchase #2	$167.53	5.555%	$176.8363	$176.84	$176.85	$176.80
Purchase #3	$91.41	13.203%	$103.4789	$103.48	$103.50	$103.50
Purchase #4	$30.49	9.462%	$33.375	$33.38	$33.40	$33.40
Purchase #5	$91.85	7.174%	$98.4393	$98.44	$98.45	$98.40
Purchase #6	$14.87	4.712%	$15.5707	$15.57	$15.55	$15.60
Purchase #7	$132.83	13.329%	$150.5349	$150.53	$150.55	$150.50
7 purchase totals =	$554.86		$605.5872	$605.59	$605.65	$605.60