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	$105.45	4.686%	$110.3914	$110.39	$110.40	$110.40
Purchase #2	$81.94	4.460%	$85.5945	$85.59	$85.60	$85.60
Purchase #3	$209.89	13.778%	$238.8086	$238.81	$238.80	$238.80
Purchase #4	$103.66	7.331%	$111.2593	$111.26	$111.25	$111.30
Purchase #5	$208.79	6.110%	$221.5471	$221.55	$221.55	$221.50
Purchase #6	$114.50	12.117%	$128.374	$128.37	$128.35	$128.40
Purchase #7	$219.94	10.701%	$243.4758	$243.48	$243.50	$243.50
7 purchase totals =	$1,044.17		$1,139.4507	$1,139.45	$1,139.45	$1,139.50