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	$99.60	9.629%	$109.1905	$109.19	$109.20	$109.20
Purchase #2	$30.27	3.652%	$31.3755	$31.38	$31.40	$31.40
Purchase #3	$101.40	10.531%	$112.0784	$112.08	$112.10	$112.10
Purchase #4	$129.43	10.852%	$143.4757	$143.48	$143.50	$143.50
Purchase #5	$171.51	11.781%	$191.7156	$191.72	$191.70	$191.70
Purchase #6	$196.55	9.525%	$215.2714	$215.27	$215.25	$215.30
Purchase #7	$82.82	10.791%	$91.7571	$91.76	$91.75	$91.80
7 purchase totals =	$811.58		$894.8642	$894.88	$894.90	$895.00