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	$160.28	12.578%	$180.44	$180.44	$180.45	$180.40
Purchase #2	$124.59	5.383%	$131.2967	$131.30	$131.30	$131.30
Purchase #3	$250.61	3.108%	$258.399	$258.40	$258.40	$258.40
Purchase #4	$83.97	12.381%	$94.3663	$94.37	$94.35	$94.40
Purchase #5	$193.47	13.871%	$220.3062	$220.31	$220.30	$220.30
Purchase #6	$71.45	13.175%	$80.8635	$80.86	$80.85	$80.90
Purchase #7	$198.38	5.168%	$208.6323	$208.63	$208.65	$208.60
7 purchase totals =	$1,082.75		$1,174.3040	$1,174.31	$1,174.30	$1,174.30