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	$16.67	11.131%	$18.5255	$18.53	$18.55	$18.50
Purchase #2	$240.39	11.533%	$268.1142	$268.11	$268.10	$268.10
Purchase #3	$188.69	13.318%	$213.8197	$213.82	$213.80	$213.80
Purchase #4	$210.40	11.126%	$233.8091	$233.81	$233.80	$233.80
Purchase #5	$80.58	11.469%	$89.8217	$89.82	$89.80	$89.80
Purchase #6	$93.82	6.103%	$99.5458	$99.55	$99.55	$99.50
Purchase #7	$20.78	9.435%	$22.7406	$22.74	$22.75	$22.70
7 purchase totals =	$851.33		$946.3766	$946.38	$946.35	$946.20