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	$5.46	12.573%	$6.1465	$6.15	$6.15	$6.10
Purchase #2	$92.64	12.871%	$104.5637	$104.56	$104.55	$104.60
Purchase #3	$164.79	4.209%	$171.726	$171.73	$171.75	$171.70
Purchase #4	$48.90	12.187%	$54.8594	$54.86	$54.85	$54.90
Purchase #5	$168.90	8.219%	$182.7819	$182.78	$182.80	$182.80
Purchase #6	$17.79	6.373%	$18.9238	$18.92	$18.90	$18.90
Purchase #7	$127.51	9.268%	$139.3276	$139.33	$139.35	$139.30
7 purchase totals =	$625.99		$678.3289	$678.33	$678.35	$678.30