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	$213.25	6.110%	$226.2796	$226.28	$226.30	$226.30
Purchase #2	$103.55	6.781%	$110.5717	$110.57	$110.55	$110.60
Purchase #3	$240.57	12.357%	$270.2972	$270.30	$270.30	$270.30
Purchase #4	$132.88	7.187%	$142.4301	$142.43	$142.45	$142.40
Purchase #5	$144.56	12.418%	$162.5115	$162.51	$162.50	$162.50
Purchase #6	$136.64	3.853%	$141.9047	$141.90	$141.90	$141.90
Purchase #7	$44.62	4.766%	$46.7466	$46.75	$46.75	$46.70
7 purchase totals =	$1,016.07		$1,100.7414	$1,100.74	$1,100.75	$1,100.70