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	$36.77	9.244%	$40.169	$40.17	$40.15	$40.20
Purchase #2	$190.48	8.561%	$206.787	$206.79	$206.80	$206.80
Purchase #3	$247.53	10.603%	$273.7756	$273.78	$273.80	$273.80
Purchase #4	$114.39	11.828%	$127.92	$127.92	$127.90	$127.90
Purchase #5	$111.86	5.292%	$117.7796	$117.78	$117.80	$117.80
Purchase #6	$167.27	7.379%	$179.6129	$179.61	$179.60	$179.60
Purchase #7	$182.63	8.772%	$198.6503	$198.65	$198.65	$198.70
7 purchase totals =	$1,050.93		$1,144.6944	$1,144.70	$1,144.70	$1,144.80