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	$120.37	7.417%	$129.2978	$129.30	$129.30	$129.30
Purchase #2	$209.71	12.720%	$236.3851	$236.39	$236.40	$236.40
Purchase #3	$119.54	12.602%	$134.6044	$134.60	$134.60	$134.60
Purchase #4	$227.60	9.193%	$248.5233	$248.52	$248.50	$248.50
Purchase #5	$174.60	12.342%	$196.1491	$196.15	$196.15	$196.10
Purchase #6	$164.39	4.223%	$171.3322	$171.33	$171.35	$171.30
Purchase #7	$250.51	13.501%	$284.3314	$284.33	$284.35	$284.30
7 purchase totals =	$1,266.72		$1,400.6233	$1,400.62	$1,400.65	$1,400.50