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	$159.74	7.211%	$171.2589	$171.26	$171.25	$171.30
Purchase #2	$184.83	7.566%	$198.8142	$198.81	$198.80	$198.80
Purchase #3	$150.62	4.168%	$156.8978	$156.90	$156.90	$156.90
Purchase #4	$118.60	4.412%	$123.8326	$123.83	$123.85	$123.80
Purchase #5	$162.78	7.350%	$174.7443	$174.74	$174.75	$174.70
Purchase #6	$101.97	12.337%	$114.55	$114.55	$114.55	$114.60
Purchase #7	$133.93	12.534%	$150.7168	$150.72	$150.70	$150.70
7 purchase totals =	$1,012.47		$1,090.8146	$1,090.81	$1,090.80	$1,090.80