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	$11.80	6.243%	$12.5367	$12.54	$12.55	$12.50
Purchase #2	$185.28	13.294%	$209.9111	$209.91	$209.90	$209.90
Purchase #3	$192.99	9.567%	$211.4534	$211.45	$211.45	$211.50
Purchase #4	$248.35	10.731%	$275.0004	$275.00	$275.00	$275.00
Purchase #5	$211.29	7.581%	$227.3079	$227.31	$227.30	$227.30
Purchase #6	$53.55	11.676%	$59.8025	$59.80	$59.80	$59.80
Purchase #7	$227.75	6.673%	$242.9478	$242.95	$242.95	$242.90
7 purchase totals =	$1,131.01		$1,238.9598	$1,238.96	$1,238.95	$1,238.90