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	$123.33	3.396%	$127.5183	$127.52	$127.50	$127.50
Purchase #2	$211.47	13.406%	$239.8197	$239.82	$239.80	$239.80
Purchase #3	$48.63	13.799%	$55.3405	$55.34	$55.35	$55.30
Purchase #4	$6.73	13.845%	$7.6618	$7.66	$7.65	$7.70
Purchase #5	$158.59	13.630%	$180.2058	$180.21	$180.20	$180.20
Purchase #6	$82.27	10.315%	$90.7562	$90.76	$90.75	$90.80
Purchase #7	$250.88	13.377%	$284.4402	$284.44	$284.45	$284.40
7 purchase totals =	$881.90		$985.7425	$985.75	$985.70	$985.70