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	$26.92	3.676%	$27.9096	$27.91	$27.90	$27.90
Purchase #2	$123.38	7.140%	$132.1893	$132.19	$132.20	$132.20
Purchase #3	$237.39	10.199%	$261.6014	$261.60	$261.60	$261.60
Purchase #4	$248.34	3.673%	$257.4615	$257.46	$257.45	$257.50
Purchase #5	$96.25	3.752%	$99.8613	$99.86	$99.85	$99.90
Purchase #6	$15.33	3.545%	$15.8734	$15.87	$15.85	$15.90
Purchase #7	$87.93	13.576%	$99.8674	$99.87	$99.85	$99.90
7 purchase totals =	$835.54		$894.7639	$894.76	$894.70	$894.90