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	$91.28	13.747%	$103.8283	$103.83	$103.85	$103.80
Purchase #2	$35.45	6.679%	$37.8177	$37.82	$37.80	$37.80
Purchase #3	$245.52	3.424%	$253.9266	$253.93	$253.95	$253.90
Purchase #4	$164.91	11.374%	$183.6669	$183.67	$183.65	$183.70
Purchase #5	$51.94	10.432%	$57.3584	$57.36	$57.35	$57.40
Purchase #6	$38.71	8.819%	$42.1238	$42.12	$42.10	$42.10
Purchase #7	$107.85	10.788%	$119.4849	$119.48	$119.50	$119.50
7 purchase totals =	$735.66		$798.2066	$798.21	$798.20	$798.20