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	$93.69	6.327%	$99.6178	$99.62	$99.60	$99.60
Purchase #2	$113.48	4.328%	$118.3914	$118.39	$118.40	$118.40
Purchase #3	$168.61	9.155%	$184.0462	$184.05	$184.05	$184.00
Purchase #4	$195.35	6.302%	$207.661	$207.66	$207.65	$207.70
Purchase #5	$214.76	3.594%	$222.4785	$222.48	$222.50	$222.50
Purchase #6	$185.50	3.288%	$191.5992	$191.60	$191.60	$191.60
Purchase #7	$38.75	8.599%	$42.0821	$42.08	$42.10	$42.10
7 purchase totals =	$1,010.14		$1,065.8762	$1,065.88	$1,065.90	$1,065.90