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	$37.38	12.356%	$41.9987	$42.00	$42.00	$42.00
Purchase #2	$87.36	13.621%	$99.2593	$99.26	$99.25	$99.30
Purchase #3	$224.97	6.137%	$238.7764	$238.78	$238.80	$238.80
Purchase #4	$213.35	11.440%	$237.7572	$237.76	$237.75	$237.80
Purchase #5	$40.36	12.616%	$45.4518	$45.45	$45.45	$45.50
Purchase #6	$171.28	5.354%	$180.4503	$180.45	$180.45	$180.50
Purchase #7	$154.62	7.177%	$165.7171	$165.72	$165.70	$165.70
7 purchase totals =	$929.32		$1,009.4108	$1,009.42	$1,009.40	$1,009.60