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	5.710%	$130.3721	$130.37	$130.35	$130.40
Purchase #2	$240.38	11.610%	$268.2881	$268.29	$268.30	$268.30
Purchase #3	$31.60	3.648%	$32.7528	$32.75	$32.75	$32.80
Purchase #4	$177.56	4.558%	$185.6532	$185.65	$185.65	$185.70
Purchase #5	$27.93	11.569%	$31.1612	$31.16	$31.15	$31.20
Purchase #6	$151.30	13.375%	$171.5364	$171.54	$171.55	$171.50
Purchase #7	$31.43	4.622%	$32.8827	$32.88	$32.90	$32.90
7 purchase totals =	$783.53		$852.6465	$852.64	$852.65	$852.80