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	$156.42	13.512%	$177.5555	$177.56	$177.55	$177.60
Purchase #2	$127.29	11.839%	$142.3599	$142.36	$142.35	$142.40
Purchase #3	$191.56	9.112%	$209.0149	$209.01	$209.00	$209.00
Purchase #4	$123.90	6.665%	$132.1579	$132.16	$132.15	$132.20
Purchase #5	$48.56	7.355%	$52.1316	$52.13	$52.15	$52.10
Purchase #6	$43.93	3.803%	$45.6007	$45.60	$45.60	$45.60
Purchase #7	$73.70	6.612%	$78.573	$78.57	$78.55	$78.60
7 purchase totals =	$765.36		$837.3935	$837.39	$837.35	$837.50