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	$180.40	3.404%	$186.5408	$186.54	$186.55	$186.50
Purchase #2	$156.73	7.791%	$168.9408	$168.94	$168.95	$168.90
Purchase #3	$5.73	6.521%	$6.1037	$6.10	$6.10	$6.10
Purchase #4	$212.91	8.759%	$231.5588	$231.56	$231.55	$231.60
Purchase #5	$205.96	6.462%	$219.2691	$219.27	$219.25	$219.30
Purchase #6	$125.70	13.464%	$142.6242	$142.62	$142.60	$142.60
Purchase #7	$49.70	9.203%	$54.2739	$54.27	$54.25	$54.30
7 purchase totals =	$937.13		$1,009.3113	$1,009.30	$1,009.25	$1,009.30