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	$28.84	9.116%	$31.4691	$31.47	$31.45	$31.50
Purchase #2	$138.43	8.577%	$150.3031	$150.30	$150.30	$150.30
Purchase #3	$57.73	6.836%	$61.6764	$61.68	$61.70	$61.70
Purchase #4	$171.97	4.377%	$179.4971	$179.50	$179.50	$179.50
Purchase #5	$29.96	4.382%	$31.2728	$31.27	$31.25	$31.30
Purchase #6	$54.91	6.788%	$58.6373	$58.64	$58.65	$58.60
Purchase #7	$150.96	7.660%	$162.5235	$162.52	$162.50	$162.50
7 purchase totals =	$632.80		$675.3793	$675.38	$675.35	$675.40