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	$159.31	12.534%	$179.2779	$179.28	$179.30	$179.30
Purchase #2	$227.80	7.117%	$244.0125	$244.01	$244.00	$244.00
Purchase #3	$203.47	7.349%	$218.423	$218.42	$218.40	$218.40
Purchase #4	$65.65	8.202%	$71.0346	$71.03	$71.05	$71.00
Purchase #5	$25.78	6.831%	$27.541	$27.54	$27.55	$27.50
Purchase #6	$231.42	3.673%	$239.9201	$239.92	$239.90	$239.90
Purchase #7	$133.64	7.243%	$143.3195	$143.32	$143.30	$143.30
7 purchase totals =	$1,047.07		$1,123.5286	$1,123.52	$1,123.50	$1,123.40