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	$41.51	13.506%	$47.1163	$47.12	$47.10	$47.10
Purchase #2	$136.85	3.469%	$141.5973	$141.60	$141.60	$141.60
Purchase #3	$121.39	13.608%	$137.9088	$137.91	$137.90	$137.90
Purchase #4	$164.48	8.540%	$178.5266	$178.53	$178.55	$178.50
Purchase #5	$177.87	5.294%	$187.2864	$187.29	$187.30	$187.30
Purchase #6	$215.96	7.145%	$231.3903	$231.39	$231.40	$231.40
Purchase #7	$153.27	9.355%	$167.6084	$167.61	$167.60	$167.60
7 purchase totals =	$1,011.33		$1,091.4341	$1,091.45	$1,091.45	$1,091.40