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	$212.38	11.388%	$236.5658	$236.57	$236.55	$236.60
Purchase #2	$31.86	12.639%	$35.8868	$35.89	$35.90	$35.90
Purchase #3	$114.47	11.797%	$127.974	$127.97	$127.95	$128.00
Purchase #4	$249.65	12.747%	$281.4729	$281.47	$281.45	$281.50
Purchase #5	$161.26	4.554%	$168.6038	$168.60	$168.60	$168.60
Purchase #6	$37.70	8.339%	$40.8438	$40.84	$40.85	$40.80
Purchase #7	$104.33	7.592%	$112.2507	$112.25	$112.25	$112.30
7 purchase totals =	$911.65		$1,003.5978	$1,003.59	$1,003.55	$1,003.70