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	$238.26	8.611%	$258.7766	$258.78	$258.80	$258.80
Purchase #2	$170.27	11.247%	$189.4203	$189.42	$189.40	$189.40
Purchase #3	$131.42	5.280%	$138.359	$138.36	$138.35	$138.40
Purchase #4	$209.33	9.631%	$229.4906	$229.49	$229.50	$229.50
Purchase #5	$56.47	4.504%	$59.0134	$59.01	$59.00	$59.00
Purchase #6	$18.30	5.427%	$19.2931	$19.29	$19.30	$19.30
Purchase #7	$134.59	3.675%	$139.5362	$139.54	$139.55	$139.50
7 purchase totals =	$958.64		$1,033.8892	$1,033.89	$1,033.90	$1,033.90