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	$113.61	13.463%	$128.9053	$128.91	$128.90	$128.90
Purchase #2	$228.48	13.517%	$259.3636	$259.36	$259.35	$259.40
Purchase #3	$164.93	9.825%	$181.1344	$181.13	$181.15	$181.10
Purchase #4	$6.89	7.107%	$7.3797	$7.38	$7.40	$7.40
Purchase #5	$206.74	10.214%	$227.8564	$227.86	$227.85	$227.90
Purchase #6	$145.68	11.533%	$162.4813	$162.48	$162.50	$162.50
Purchase #7	$44.78	8.549%	$48.6082	$48.61	$48.60	$48.60
7 purchase totals =	$911.11		$1,015.7289	$1,015.73	$1,015.75	$1,015.80