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	$104.70	5.409%	$110.3632	$110.36	$110.35	$110.40
Purchase #2	$242.74	8.471%	$263.3025	$263.30	$263.30	$263.30
Purchase #3	$85.47	4.705%	$89.4914	$89.49	$89.50	$89.50
Purchase #4	$35.97	12.568%	$40.4907	$40.49	$40.50	$40.50
Purchase #5	$12.48	7.164%	$13.3741	$13.37	$13.35	$13.40
Purchase #6	$212.48	4.585%	$222.2222	$222.22	$222.20	$222.20
Purchase #7	$21.39	5.838%	$22.6387	$22.64	$22.65	$22.60
7 purchase totals =	$715.23		$761.8828	$761.87	$761.85	$761.90