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	$34.89	13.185%	$39.4902	$39.49	$39.50	$39.50
Purchase #2	$206.27	8.714%	$224.2444	$224.24	$224.25	$224.20
Purchase #3	$196.80	6.119%	$208.8422	$208.84	$208.85	$208.80
Purchase #4	$243.44	4.116%	$253.46	$253.46	$253.45	$253.50
Purchase #5	$141.73	4.800%	$148.533	$148.53	$148.55	$148.50
Purchase #6	$188.33	3.240%	$194.4319	$194.43	$194.45	$194.40
Purchase #7	$16.33	6.765%	$17.4347	$17.43	$17.45	$17.40
7 purchase totals =	$1,027.79		$1,086.4364	$1,086.42	$1,086.50	$1,086.30