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	$13.96	13.143%	$15.7948	$15.79	$15.80	$15.80
Purchase #2	$154.67	6.130%	$164.1513	$164.15	$164.15	$164.20
Purchase #3	$18.30	6.780%	$19.5407	$19.54	$19.55	$19.50
Purchase #4	$70.99	10.851%	$78.6931	$78.69	$78.70	$78.70
Purchase #5	$27.28	7.173%	$29.2368	$29.24	$29.25	$29.20
Purchase #6	$159.81	7.200%	$171.3163	$171.32	$171.30	$171.30
Purchase #7	$25.87	6.315%	$27.5037	$27.50	$27.50	$27.50
7 purchase totals =	$470.88		$506.2367	$506.23	$506.25	$506.20