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	$50.52	4.697%	$52.8929	$52.89	$52.90	$52.90
Purchase #2	$48.93	7.420%	$52.5606	$52.56	$52.55	$52.60
Purchase #3	$203.46	11.695%	$227.2546	$227.25	$227.25	$227.30
Purchase #4	$43.70	8.272%	$47.3149	$47.31	$47.30	$47.30
Purchase #5	$178.28	6.276%	$189.4689	$189.47	$189.45	$189.50
Purchase #6	$208.48	11.807%	$233.0952	$233.10	$233.10	$233.10
Purchase #7	$112.60	9.323%	$123.0977	$123.10	$123.10	$123.10
7 purchase totals =	$845.97		$925.6848	$925.68	$925.65	$925.80