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	$249.35	10.783%	$276.2374	$276.24	$276.25	$276.20
Purchase #2	$241.58	11.726%	$269.9077	$269.91	$269.90	$269.90
Purchase #3	$159.51	6.456%	$169.808	$169.81	$169.80	$169.80
Purchase #4	$29.46	5.742%	$31.1516	$31.15	$31.15	$31.20
Purchase #5	$99.56	5.736%	$105.2708	$105.27	$105.25	$105.30
Purchase #6	$77.84	4.436%	$81.293	$81.29	$81.30	$81.30
Purchase #7	$75.53	12.704%	$85.1253	$85.13	$85.15	$85.10
7 purchase totals =	$932.83		$1,018.7938	$1,018.80	$1,018.80	$1,018.80